If your iPhone is locked to a particular carrier, it can be truly frustrating. Some iPhones will only work with a SIM card provided to the carrier they're locked to – O2, EE or Vodafone, for example. But there are ways to unlock youriPhone 4, iPhone 4S, iPhone 5, iPhone 5S, iPhone 5C, iPhone 6 or iPhone 6 Plus so that you can use any SIM card. Here, we show you how. See also: iPhone 6 vs iPhone 6 Plus comparison review
How to unlock an iPhone
Some iPhones are easier to unlock than others, depending on the carrier and the phone's circumstances. Your mobile phone provider may be able to unlock the phone for free, and this is more likely if your iPhone's original contract has ended. However, it's trickier to get your iPhone unlocked if your contract is still valid.
Unlocking your iPhone is completely legal if you purchased the device unsubsidised of have finished paying for your contract. However, if you're still paying for your contract, you technically don't own the iPhone yet, so you really should check with your carrier before unlocking it.
Of course, not every iPhone needs unlocking. Most of the iPhones Apple sells in the UK work on all networks. It's the iPhones that you have purchased from a carrier that are more likely to be locked to that network.
You'll discover that your iPhone has been locked to a particular network if you insert a SIM card from another network into the iPhone and attempt to make a call. If it doesn't work, it's likely that your iPhone is locked to your network.
Don't forget that the iPhone 4S uses a MicroSIM, which is bigger than the iPhone 5, iPhone 5S, iPhone 5C, and iPhone 6 so be sure you're using the correct sized SIM. See:iPhone 5s vs iPhone 5C comparison review.
Here's a list of popular UK carriers and how to go about getting your iPhone unlocked by them:
Three also has an online form to allow you to unlock your iPhone.
Virgin Mobile: Call 780 from the iPhone or 0345 6000 789 from any other phone
Tesco: Tesco says it will only provide you with a code to unlock your iPhone if you've been with the carrier for 12 months or if you've completed your contract. If that's you, you'll need to call 0800 0321 320
EE (including Orange and T-Mobile): To unlock your EE iPhone, you'll need to have had your account for at least six months, and you'll need to have paid all of your bills to date. EE says it'll take up to 20 days to unlock your iPhone, and it'll cost you £20.42.
When your carrier has agreed to unlock your iPhone and has processed your request, you'll need to replace the old SIM card with a SIM card of the carrier you wish to change to. Make sure your iPhone is off when you do this, and when your turn your iPhone back on it will talk you through any further updates that may be required.
If you don't have the original SIM card but have requested for your iPhone to be unlocked by the original carrier, you'll need to reset your device.
Make sure you back up your iPhone by connecting it to your computer and using iTunes to perform a backup, and then completely reset your device by going to Settings > General > Reset > Erase All Content and Settings. Everything will be wiped from your iPhone following this process, so backing up your iPhone is EXTREMELY important to do first.
You can now complete the setup assistant on your iPhone and restore your iPhone from the backup you created. Insert your new SIM card. This should mean that your iPhone is now unlocked.
You don't have to go through your carrier to unlock your iPhone, though we think it's better if you can. If that's not possible, you can use an unlocking service. You might know of an unlocking service in a retail area local to you, or you can visit MobileUnlocked.com or OfficialUnlockPhone.co.uk. They'll charge you a small fee, and we'd recommend avoiding anyone who attempts to charge you more than £25 to unlock your iPhone.