Frequently Asked Questions
Help and advice on all topics related to switching to SIM-only
We aim to make it easier than ever to switch your mobile phone tariff and save money.
Is there a question you can’t find the answer to? Ask away!
How do I work out how much back up space I need?▲
Working out how much back up space you need for your phone or other device can leave you second-guessing yourself. Many people simply look at how much space they’re using and then pick a backup plan of the same size.
Realistically you need a lot more than that to account for additional backups and all the extra files you add to your phone over time.
To accurately calculate how much back up space you need, firstly take a look at your phone’s total storage capacity, which is usually found in the Settings menu and listed in gigabytes (GB).
Don’t forget to account for any additional expandable memory cards if you have an Android phone.
Next, take that number and multiply it by either three or four. This ensures you have enough space for multiple backups plus some left over as a buffer just in case you need it.
How often should I back up my phone?▲
The frequency of your phone backups broadly depends on how often you add new files to your phone and how important they are.
For example, if you’re constantly taking family photos, or recording important notes, you’ll want to back up your phone quite often just in case the worst happens.
Many people find backing up their phone once a week is more than adequate.
If you’re using your phone for business purposes, and you get work emails or documents to your device, you may find more frequent backups are necessary.
You can also ensure that your backups are timed for convenience, i.e. not in your core working hours or set to complete after a particular project. If you don’t have automatic backups scheduled on your phone, try setting a reminder in your calendar or to do list app to ensure you don’t forget.
What does ‘unlocked’ mean on a phone?▲
What does ‘unlocked’ mean?
When a phone is ‘unlocked’ it can be used with SIM cards from any network.
A ‘locked’ phone is restricted to only use SIMs and contracts from a single network – usually the network that supplied the phone.
If a phone is locked, it is harder to switch to the perfect SIM Only deal once your contract expires as you’ll still be restricted to offers from your current network.
You can check if your phone is locked by inserting a SIM from a different network and trying to make a call. If the call fails, your phone’s locked.
Smartphones can be unlocked by contacting your network operator and asking them to unlock your device. This service is usually free although it could cost up to £19.99.
Before you call, you’ll need to note down your phone’s 15-digit IMEI number by entering *#060# into the keypad.
How do I find my SIM’s phone number?▲
To find out your own phone number you can check your phone’s contact list, settings menu or contact your network operator.
Many phones will store your number in the contact list, and it is usually under the heading My Number.
If your number isn’t in the contact list, you can check your phone’s Settings menu. The following instructions are for Android devices, but other operating systems will have similar steps:
Open the Settings menu, select About Device or About Phone, then select Status or Phone Identity.Find My Phone Number on the list of options and tap it to display your number.
The third option is to call your network’s customer service line and simply ask them for your phone number.
If you call your network operator be sure to have a note of your SIM card’s serial number ready, even if you’re calling them with that SIM, as they may ask you for it. You can either find the serial number printed directly on the back of your SIM, or check this quick how-to guide.
How do I use my PAC code?▲
Once you have your PAC code all that’s left to do is give it to your new network operator so they can start transferring your number.
Many networks give you the option to set up a number transfer when you’re purchasing a new SIM Only deal, so if you have your PAC code ready before buying you can make the number transfer almost seamless.
If you already have your SIM, all you have to do is call your new network, ask for a number transfer and give them the PAC code for your old number. Some networks allow you to do this online by logging in to your customer account.
Once you give them your PAC, the transfer will begin. This process can take up to 24 hours and you will lose service until it is completed.
How do I get my PAC code?▲
You’ll need to call your current network operator to request a PAC code for your SIM card. Some networks, such as giffgaff, have an online service where you can request a PAC but calling your network is often the easier option.
The process of requesting a PAC is usually automated, so you’ll have to navigate to the relevant section of your network’s automated answering service. If that option isn’t available you can always talk to a human operator and request a PAC from there.
It may take up to two working days to receive your PAC and it will expire 30 days after you requested it.
Your PAC is normally sent to you via text message but it’s a good idea to make a note of it separately as you will need to have it to hand when you’re sorting out the transfer with your new network.
What is a SIM serial number?▼
Every SIM has a unique serial number which is used to identify it. You’ll need to know your SIM’s serial number to perform a SIM swap and transfer your number to a different SIM card on the same network.
To transfer numbers between SIMs on different network, you’ll instead need a PAC (Porting Authorisation Code).
You can find the serial number printed directly onto the SIM itself. The number will be between 12 and 20 digits long, so it may be printed over several lines even though it is all one number.
If the serial number isn’t printed on your SIM card, you will be able to find it on the packaging or in the documentation of your SIM.
If you are unable to find your SIM serial number, you may be able to get it from your network by contacting customer support and giving the phone number associated with your SIM.
What does PAC mean on a phone?▼
A PAC is a Porting Authorisation Code – it is used to transfer a phone number between SIM cards on different networks. The PAC is unique to your SIM card and you can request one from your network any time you plan on changing numbers.
Be aware that a PAC will expire after 30 days, so if you don’t change numbers within that time you’ll have to request a new one the next time you’re thinking about switching network.
Using a PAC is an easy way to transfer your number and the entire process is completely free providing you have fulfilled the contract with your old network.
The PAC code is only used to transfer numbers between different network operators – to transfer a number onto a new SIM from your existing network you’re instead going to need the SIM serial number for a SIM swap.
How do I use my PUK code?▼
If your phone is asking for a PUK code, it means your SIM has been blocked by your network.
If you don’t already have it, you can acquire a PUK code from your network either online or by calling customer support. All the current UK network Customer Helpline numbers are here.
Once you have your PUK code, key it into your device when prompted (it’s typically the only thing you can do on a device with a blocked SIM).
You get 10 attempts to input your PUK code, which should be plenty, but be aware that inputting it incorrectly 10 times will permanently disable your SIM and you’ll have to order a replacement.
When the PUK is input correctly, your SIM will be immediately unblocked and you will regain access to all of the features on your device.
How do I get my PUK code?▼
If your SIM card has been blocked, you can get it unblocked by inputting your SIM’s PUK code.
To find your PUK code, you’ll have to contact your network, either by phone or through the network’s website. Find Customer Helpline numbers for all UK networks here.
If you’re requesting a PUK by phone you’ll have to answer some security questions to confirm your identity.
These will either be questions you set up when you created your account, such as “what was the name of your first pet?”, or details on your payment and personal information.
Once your identity is confirmed, the network will provide a PUK code to unblock your SIM.
Some networks make the process easier by providing PUK codes online. Go to your network’s website, log into your customer account and navigate to the page for unblocking your SIM – you can grab the code there.
What does PUK mean on a phone?▼
A PUK is a Personal Unblocking Key and it is used to unblock your phone, typically when a SIM PIN has been input incorrectly too many times.
You can’t use a blocked SIM until the right PUK code has been keyed into the device.
Some people confuse a PUK code with a PAC code – a PAC code is what you need to get from your network if you want to transfer your mobile number to another network.
You will have to contact your network operator for a PUK code and confirm your details. Depending on your network, you may be able to get your PUK code online by logging into your customer account.
Some networks include the PUK code in your SIM card’s documentation, so it’s useful to keep hold of it in case your SIM ever becomes blocked.
If a PUK code is input incorrectly 10 times, the SIM card will be permanently erased and you’ll need to order a replacement from your network operator, so don’t try to guess it.
What is a SIM PIN code?▼
A SIM PIN code is an additional security measure that you can activate to keep your data safe.
The PIN is a 4-digit number that is saved directly to your SIM card, so it follows the SIM even if you switch it into a new phone or another device.
You can lock a phone with a passcode, but if you don’t have a SIM PIN you can’t protect your SIM if it is stolen.
If the SIM PIN is entered incorrectly 3 times, your SIM is blocked and cannot be used until a PUK (Personal Unblocking Key) is input, which you can get by contacting your network.
If a PUK is entered incorrectly 10 times then any data, contacts, files or photos on the SIM will be permanently erased.
To set a SIM PIN, go to the Security settings on your phone and set up a SIM card lock. You’ll need the default PIN, which you can get from your network or find in your SIM’s packaging or documentation (if you kept onto it). You can then set a 4-digit code to lock your SIM with.
What is a SIM swap?▼
A SIM swap moves your phone number, minutes and credit onto a different SIM card.
It’s a quick way of replacing your SIM card if it is lost or damaged.
You can only swap between SIMs on the same network, but if you keep a spare SIM card handy, you can be up and running in less than 24 hours with a SIM swap.
Visit your network’s website for specific instructions on how to perform a swap, but the general process involves texting your operator with the serial number of the SIM you want to swap to, or filling out an online form.
You’ll find the SIM serial number printed on the SIM card itself and if you need a replacement SIM to swap to, you can order one from your network operator.
After completing the process, it’s simply a matter of waiting for your network to complete the swap.
This part usually takes less than 24 hours, but your SIM will not get service until it’s completed so we’d recommend you don’t perform the swap if you’ll need your phone urgently the next day.
My SIM is faulty, what do I do?▼
If you have a faulty or broken SIM card, you can order a replacement SIM from your network or get one from your local store. With a replacement SIM, you will keep your number and won’t lose any credit or minutes.
Ordering a new SIM can take several days, so if you can get your hands on a SIM from the same network a faster option is to perform a SIM swap.
You’ll need the serial number printed on your SIM to perform a SIM swap and the swap can be performed via text or online through your network’s website.
Some networks will not transfer your number onto the replacement SIM when you order, so you’ll have to do a SIM swap yourself when your replacement arrives.
What is an MVNO network?▼
An MVNO is a Mobile Virtual Network Operator – a type of network that doesn’t own or maintain any of its mobile infrastructure – instead piggybacking on the networks that do own the infrastructure.
Some MVNOs are: giffgaff, iD Mobile, Virgin Mobile and Tesco Mobile.
At the moment only the Big Four UK networks actually own masts which deliver mobile signals.
These are EE, O2, Three and Vodafone.
Every mobile ‘network’ that isn’t one of those four is actually an MVNO.
Because MVNOs have no control over the infrastructure, the quality of phone calls and 4G you’re going to get is entirely dependant on the network they operate under. Find out here which SIM Only deals are on which network.
Although the mobile service of an MVNO depends on the network they’re attached to, their customer service and contract deals are entirely their own thing, so many people report a better experience with an MVNO than with one of the Big Four networks.
How do I find out my IMEI number?▼
An IMEI number is a 15-digit code that is unique to each individual handset. It can be used to identify your phone and ‘block’ it from a network – handy for disabling your phone if it is lost or stolen.
Knowing your IMEI number is unlikely to help get your phone back, but it can at least render the device useless for the thief.
On older phones, you can find the IMEI number underneath the battery on a label with several barcodes (the 15 digit number is your IMEI).
For newer devices, you can find the IMEI by looking in your phone’s general settings or by dialling *#06# – the IMEI will appear on your screen.
The IMEI number will only block the handset, not the SIM card inside it.
You may be able to get your network operator to block the SIM card in addition to your handset, but an easier way to protect your SIM is with a SIM PIN code, which can be activated in your phone’s settings.
What does ‘unlocked’ mean?▼
An unlocked phone is compatible with SIM cards from any network, so you can freely switch between SIM Only deals on different networks without needing to change your handset.
Some phones, especially those that are included with monthly contracts, are ‘locked’ to a specific network and will only work with SIM cards from that same network.
This makes it harder to switch to a SIM Only contract from a different network further down the road.
If your phone is locked, you can call your network and have the phone unlocked for use with any SIM.
Be aware that many networks will charge you to unlock a handset (ranging from £9 to £20) and require you to have completed the minimum term of your contract.
Customer Helpline numbers for all UK networks▼
Finding a customer support number for many networks shouldn’t mean a frustrating search through FAQs and endless lists.
The chart below is a handy reference that keeps the customer service numbers of all UK networks in one place.
You can dial any of the numbers from your mobile or landline phone.
What are public WiFi hotspots and which networks offer them?▼
A WiFi hotspot is a place where anyone can connect and enjoy broadband-quality internet in public places.
Many businesses and venues offer free WiFi to draw in customers.
By connecting to a WiFi hotspot, you can use the internet without worrying about your mobile data allowance.
O2 deliver many hotspots around the country and they’re free for anyone to use. If you’re an O2 customer, simply input your phone number when connecting. Everyone else will need to register on the O2 website to start accessing free WiFi.
All network operators offer free WiFi on the London Underground with Virgin Media’s hotspots.
Virgin Mobile plans give access to all of Virgin Media’s WiFi – over 250,000 hotspots around the country.
EE and Vodafone offer plans that use BT Openzone hotspots. If you know you’re often in range of one, it could be worth paying more for a hotspot plan to keep your data usage down.
What is roaming?▼
When you use your phone abroad, you are beyond the reach of your home network and your phone has to connect to foreign networks instead. This is known as roaming.
Using foreign networks often involves paying an additional fee, called the roaming charge.
The cost of this charge changes from country to country, but a general rule is that the further you are from home, the more expensive it is to use your phone.
Roaming charges are applied when you use your phone to call, text or access the internet. They can also be applied when you receive a call or text, which means you’ll be paying for both sides of a conversation.
At the end of each month, any roaming charges you have accumulated will be added to your phone bill.