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The best O2 SIM only deals and plans in February 2021

For many, O2 SIM only deals will represent the perfect choice for their next phone. It stands as one of the four main networks with a wide range of smaller MVNO SIM only deals making use of its technology, coverage and technology.

With its long-standing history, starting off in 1985, O2 has had plenty of time to perfect its SIM only deals. Right now, it fits in neatly next to Vodafone as a very well-rounded platform.

It's not overly expensive, it has a number of big data SIM plans at affordable price points and finds itself discounted throughout the year. On top of that, to compete with increased competition from Three, Vodafone and EE, O2 has increased its presence in the world of incentives.

Including gifts like free Disney Plus subscriptions, boosts to data, half price promotions and more, O2 SIM only deals are looking the strongest that they have in a long time.

So what are the best prices? How do O2 SIM only deals compare to its competition like Three SIM only deals and Vodafone SIM only deals? We've answered all of these questions below.

Compare O2 SIM only deals:

Why choose O2? Coverage, benefits and more

O2 SIM only deals

Is O2 a good mobile network?

It is. Between 3G, 4G and now 5G,  it reaches 99% of the UK population, and it powers some household names’ networks such as Tesco Mobile and GiffGaff. You can check the coverage map here.

There are many benefits to an O2 SIM only deal. O2 offers free Wi-Fi in more than 15,000 locations throughout the UK, it has some nice goodies such as the O2 rewards loyalty and if you’re into gigs and other big-ticket events you can beat the touts thanks to the excellent O2 Priority service.

sim only deals

Are O2 SIM only deals cheaper than contract?

Yes, but also no.

We’re not being slippery here: the answer depends on a lot of different factors. If you’re reaching the end of a contract and don’t want to change your phone then yes, a SIM only deal from O2 could save you a fortune compared to starting a new contract with a new phone. 

However, buying an O2 SIMO deal and buying a handset separately might not be cheaper than a contract deal. For example if you drop £749 on an iPhone XR and get an O2 SIM only deal you might find that you’d pay the same or even slightly less if you’d got the iPhone XR on an O2 contract deal. Although of course you’d then be tied into that contract, which in most cases would last for two years.

If you’re quite keen on a new phone we’d definitely recommend checking our mobile phone deals guide too. Fierce competition means there are good deals to be found.

How to switch over to an O2 contract:

Can I keep my old number?

You can. It’s usually very easy: if you’re moving from a network that isn’t O2 you’ll need to call them up and ask for a PAC number. It’s short for Porting Authorisation Code and it tells O2 that it’s okay to use your existing number. The numbers you need are:

  • EE 07953 966 250
  • Vodafone 03333 040 191
  • Three 0333 300 3333
  • ID 0333 003 7777
  • GiffGaff 43431 from your handset
  • Virgin 0345 6000 789
  • BT 0800 800 150
  • Tesco 0345 301 4455
  • Sky 03300 412 524
  • Asda 0800 079 2732

Things are a little more complicated if you’re already an O2 customer. You’ll need to use their Keep My Number form.

O2 sim only

Is my phone unlocked? Can I use a new SIM in it?

If you’re already with O2 or your phone is from Three your phone should work happily with a new O2 SIM. However, if it’s a phone from another provider it may be locked to that network.

The easiest way to check is to try the SIM from a friend or family member’s phone (if they’re on a different network to the one you’re on). If you pop it in and your phone connects without problems, you’re good to go: you can go ahead and get your new O2 SIM card.

If not, here’s what you need to do for each network.

  • Three: nothing. All Three phones are sold unlocked.
  • EE: if it’s an iPhone and you’ve had it more than 18 months it will be unlocked automatically. If it’s a contract phone it’s free to unlock once the contract’s finished or £8.99 otherwise. Pay as you Go phones are £8.99 to unlock or free if you bought directly from EE. Second-hand devices are £8.99 to unlock.
  • Vodafone: unlocking should be free but can take around 10 days.

sim only deals from O2

What SIM card size do I need?

There are three different sizes of SIM card, and chances are your phone will use one of the two most recent ones: micro SIM (12mm x 15mm) or the even smaller nano SIM (8.8mm x 12.3mm). Older phones used the standard SIM, which was a positively porky 15mm x 25mm. If the provider doesn’t offer a triple SIM, which you can pop out until you get the size you want, you can simply request the appropriate size when you order your new SIM card.

But there's no need to get your knickers in a twist about this one. The networks and third party sellers will let you choose which SIM you need or will simply send out a triple SIM, so you'll get one of each size. Alternatively, they'll send you an adapter so you can use the incorrect SIM size in your phone.

What factors should I consider? Data, calls, texts and more:

What contract length should I get?

That’s entirely up to you. As a rule, the longer the contract the cheaper it gets: really short contracts are convenient but tend to cost more. The sweet spot is usually at the one-year mark and occasionally the two year mark much like phone contracts. use the “Contract Length” filter in our comparison chart to compare contracts of that length.


How much phone data do I need?

That’s a very good question, and we’ll answer it with another one: How much do you love Netflix and Spotify? If you rarely look up from your phone throughout the day and stream constantly, you’ll burn through data like...well a big burny thing. If all you do is instant message, you’ll hardly use any data at all. 

If you’ve been on contract you’ll already know how much data you tend to use, especially if you kept going over the data limit or ended up with tons of unused data each month. Here’s how much data typical users get through in a month.

  • 1GB: This is the cheapest option but can be a false economy if you keep busting through the limit, and you probably will: it’s best suited to occasional Maps usage and email and not much else.
  • 2-3GB: This is a better bet if you spend a lot of time messaging or on social media, but not video sites.
  • 4-8GB: This is the mid-range where a lot of people are perfectly happy: there’s enough allowance for podcasts and YouTube without spending tons of money on an allowance you didn’t use.
  • 10-16GB: We’re getting into power user territory here: the road warriors, the constant chatters, the box set streamers.
  • 20-30GB: You have lots of money, and a mobile phone glued to your face. You’d need to do a lot of streaming and downloading to need this much: we’re talking home-broadband levels of data use now.

sim only deals

Should I get unlimited calls and texts?

That depends on what you use your phone for: we barely call anybody and tend to use instant messaging instead of SMS, so unlimited calls and texts don’t matter to us. 

However, if you talk on your phone so much your friends have never seen one half of your face, unlimited calls are a great idea. Just be aware that unlimited texts doesn’t mean unlimited picture messages too: they’re still chargeable. 


Now you're in the know, scroll back to the top of the page to get hold of the O2 SIM that suits you. And if you're not sure that O2 is the right network for you, then see what the other networks have to offer in our guide to the best SIM only deals.