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There are three sizes of SIM card that you can get for your phone, and the one you need will depend on your handset. It's been a while since the traditional, so-called standard SIM 15x25mm has genuinely been the staple in new phones. Instead, any phone you've bought within the last five or so years is much more likely to require a micro 12x15mm or nano 8.
Before you purchase your new SIM, double-check the manufacturer's website to see what size you require. And if you're simply not sure, most networks now simply send out a triple SIM, so you'll get one of each size. Ever heard of PAC codes and wondered what a classic 80s arcade game had to do with telephone numbers?
It actually stands for Porting Authorisation Code, and it's the set of digits that you need to grab from your old network to let you transfer over your existing mobile number.
If you're on one of the major networks, you can see what phone number you can contact them on here:. If you want to grab a bargain SIM only plan above, but it's on your existing network then your network won't release a PAC code and you'll be forced to take a new phone number.
At least you would have, if it wasn't for this clever if convoluted work-around. You have to order a free pay-as-you-go SIM from another network. Once you have it, you can tell your old network that you're moving and they'll give you that precious PAC code. Then, once your number is registered to the substitute network, simply get another PAC code from them. Take that to your old network, and they'll move your number to your new contract. Simple - kind of! Unlike with a contract, there's a lot more flexibility available when it comes to how long your SIM only plan will last.
Two year commitments are virtually unheard of, with the norm being either one year or rolling one month contracts for ultimate flexibility.
You can often get better prices if you tie yourself in for 12 months, especially on larger data tariffs. But sticking to one month at a time means that you can effectively hand pick a new plan to suit you every 30 days or so. Because you can change your plan up more regularly than a normal, lengthier contract, it's less crucial to get this nailed from the start. But if you're thinking of grabbing a monther or just put a personal pride on getting things right first time, then we'll help you pick out the sweet spot of data for you.
Firstly, check your phone to see how much data you've been using to date, and whether you have the tendency to use more than your current allowance every month. Then, if you're still unsure, check out our guidance: Call it practicality, call it greediness, call it what you want - it's human nature to want 'unlimited' anything if offered. But you should think genuinely about whether you really need it in a world where the likes of WhatsApp and Skype let you call and text for free over wi-fi or 4G.
If you decide that a few thousand monthly minutes and texts should do you, then you could shave off some cash from your bill. While EE, O2, Vodafone and Three are generally considered the major four networks for contract plans, when it comes to SIM only there are some other key players are well worth a look.
See what we think of them below, and whether you'll get any free perks to help persuade you to sign up. Plus, we'll tell you about a couple of other SIM sellers that might be able to wrangle you an even better deal. It's one of life's many little frustrations - you sign up with a network, get your SIM up and running and then discover that you get no coverage at all in your house. Well this little pain in the neck can be avoided by using the dedicated coverage checker that most networks provide. Enter your postcode and you'll see whether your address has 2G calls, texts and email , 3G the basics plus picture messaging and faster web browsing and 4G all the powers of 3G, plus faster downloads, online gaming and media streaming coverage.
See our pick of the best deals at EE. O2's best claim for your contract is with its Priority rewards - from cheap lunch deals and pre-order privileges on gig tickets, to ad-hoc discounts and competitions. Plus, they have s of Wi-Fi hotspots in shops and cafes that you can connect to for free and save your precious data.
See our pick of the best deals at O2. Vodafone seems to have been around since mobile phones were cumbersome bricks, but they remain a major player. See our pick of the best deals at Vodafone. Three is still the only network to offer unlimited data and it often features unbeatable deals on other big data plans - that makes them a natural choice of many a data hungry smartphone addict.
And it has has just started getting generous with perks - you can get cheap dinners and free coffees through its Wuntu app. See our pick of the best deals at Three. That familiar old stalwart of telecommunications BT is so-so when it comes to SIM only tariff prices. That's unless you're already a BT broadband customer, in which case you get some really favourable prices - a fiver less than the rest of the hoi polloi.
Plus, you usually get a BT Reward Card with the majority of plans that can be spent anywhere that accepts Mastercard, the value of which depends on how much data you're in for. This is a network run and owned by Carphone Warehouse - it piggybacks on the Three network.
View this deal at iD. When you find the deal you know you want, simply add it to your basket, select a delivery option, and complete the checkout process. Short-term SIM Only contracts give you freedom and flexibility. What is a SIM only deal? Perhaps the best thing about going with Three, though, is that if you've got a 4G device you'll pay the same as you do for 3G. Check out and compare our full range of iPhone deals.
It's an excellent option if you want great value on a rolling monthly contract. They don't give you much of a data allowance to play with, but if you just want to keep your phone going and available to use for calls and texts with the occasional bit of internet use outside of your home Wi-Fi, GiffGaff is a strong offering. Virgin Mobile has been going for a long time, and some of its SIM only deals are particularly attractive.
They're all one-month rolling contracts, so you can stop paying at any time if you so wish, giving you flexibility if you want to change your plan or go for a phone-inclusive deal down the line.
The UK's biggest supermarket has been known to offer competitive - if not stellar - SIM plans, with low data prices starting at not much more than a fiver a month. Where it get's really interesting is if you download the Xtras app to an Android phone: O2 iPhone SIM only customers also quality for some great benefits, such as money-off incentives and priority booking for events at O2 venues. Three SIM only iPhone deals team great coverage and connection speeds with ample mobile internet allowance. Perhaps the best thing about going with Three, though, is that if you've got a 4G device you'll pay the same as you do for 3G.
But they do offer you the fastest 4G speeds in the UK. Looking for a phone instead? Show me: All SIM deals. Promoted deals have been lent additional visibility as a result of us securing exclusivity on a great deal, or a commercial agreement to showcase what we believe to be market-leading value to consumers. Filter your results. No contract. Unlimited texts. Only show 4G deals.
Apply filters. See deal Order from iD Mobile. Plusnet Multi SIM. See deal Order from Plusnet. See deal Order from Virgin Mobile.
Data rollover. See deal Order from Three Mobile.
Great for roaming. Unlimited Social Data. See deal Order from giffgaff. O2 Multi SIM. See deal Order from O2. See deal Order from Sky Mobile.
See deal Order from Tesco Mobile. Flexible cap on spending. Vodafone Multi SIM.