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The best unlimited data SIM only deals in September 2019

Netflix bingers, podcast addicts and Google Map navigators unite - we've rounded up the best SIM only deals that will keep you using your favourite smartphone apps without fear of exceeding data allowance limits.

Because with these unlimited data plans, there's no such thing as data allowance limits. It may seem like an extravagance, but pop a SIM with unlimited data into your mobile phone and you can start streaming, surfing and downloading to your heart's content.

And all-you-can-eat data SIM deals may be cheaper than you had imagined. Considering the heady prices they usually fetch as part of a contract mobile phone deal, getting one at the end of a two-year term or to work in a brand new SIM-free phone can be great value. But hold your horses for just one moment if you were on the lookout for an unlimited data only SIM. In our Q&A below, we'll explain why infinite data in your tablet requires a little lateral thinking.

Unlimited data SIM only deals: common questions answered

To help you decide whether or not to lay your eggs in the uncapped data basket, we've tackled some commonly asked questions about unlimited data SIMs.

Do I need unlimited data?

We'd love to be able to give you a straight yes or no to this question. but the reality is that it depends entirely on how you use your device.

The first thing to do is head to your phone's settings, locate your data usage stats and see how much you currently use a month. If you're using 3GB at the moment and can't imagine that changing any time soon, then going unlimited is a ridiculous extravagance. If your current limit is in excess of 20GB and you frequently find yourself exceeding it, then paying a few extra pounds a month for unlimited makes sense.

How expensive is it to get unlimited data?

If you're after the exact pounds, shillings and pence, then simply scroll back up to the top of this page and have a play with our price comparison chart. We've scoured the market and populated the table full of the very best SIM with unlimited data deals out there right now.

Relative to other SIM only deals, you won't be surprised to hear that all-you-can-eat data is the most expensive type of SIM plan you can buy. If you drop down to 30GB or even 100GB, you can usually save a few pounds a month and a decent sum over the course of a year.

Should I go SIM only?

Opting for a standalone SIMO plan has grown massively in popularity over the last year or so. That's because 2015 phones like the iPhone 6S and Samsung Galaxy S6 were so good that owners who have come to the end of their contracts are reluctant to part with them.

Grabbing a SIM only deal instead is an affordable way to keep using a beloved phone and delays the inevitable hunt for a pricey new mobile phone deal.

If you can afford the upfront cost, it's also worth considering grabbing and unlimited data SIM to team up with a smartphone that you buy upfront. Take the iPhone XS as a great working example. You'll have to pay more than £1,500 over the course of two years if you plump for an all-you-can-eat contract. If you can afford the eye-watering £999 for the handset and put one of our cheaper uncapped SIMs in it, then you could end up saving more than £300 over that 24 month period!

Which networks do unlimited data SIM only deals?

If you're on the likes of EE, Vodafone or O2 and were hoping to go unlimited with one of those, then we're afraid we have some bad news. At the moment, there are only a handful of players in the unlimited data game - Three, Virgin Mobile, Giffgaff, Smarty and new to the game - Vodafone.

Giffgaff often manages to trump the other two on price alone, but we have a word of warning. You can't really call Giffgaff's 'Always On' uncapped plans unlimited as speeds are throttled after you use a certain amount of data. By that, we mean that you only get 4G speeds (5 to 12 megabits per second) for those first 20GBs or streaming and surfing. Once you've breached that line, data speeds goes down to a measly 384kb between 8am and midnight.

Virgin's 'Truly Unlimited' promise means that it doesn't throttle speeds in the same way, but it's only available for customers already using Virgin broadband.

Smarty's unlimited SIM offer is the newest face on the scene. The price is competitive and there's no limit on speeds like with Giffgaff. The other bonus is that Smarty only deals in 30-day contracts, so you'll never be locked into a lengthy term.

What about unlimited data only SIM plans?

Do you like to use your tablet as a portable TV on your commute or out in the garden? Then you might be interested in getting an unlimited data only SIM to give you uncapped coverage from your chosen streaming service or subscription sports app.

Alas, neither Three, Virgin or Giffgaff offer a dedicated data only SIM with unlimited GBs.

There's a bit of a workaround, but it's not particularly satisfying. Three and Giffgaff allow you to use your smartphone as a personal hotspot. That means that you can then tether your tablet (or laptop or any other device) to your phone and make the most of the unlimited data that way instead. However, Three's personal hotspot allowance is limited to 30GB per month and Giffgaff's crippling speed restrictions kick in after 9GB.

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

Ask a friend or family member whether they're on a different network to you. If they are then grab their phone (ask them first, for heaven's sake!), take out the SIM card and put it in to yours. If the phone accepts it and lets you start using your phone with their SIM, then your phone is unlocked and you can use a new SIM with unlimited data in your phone. This should be the case for any phone where you've come to the end of a two-year contract.

If you your phone is still locked to your old network however, then you'll have to contact them and potentially pay a fee to unlock your handset to other networks. Here's how the major networks play things:

  • O2 As long as you don't own an iPhone X, 8 or 8 Plus or a Samsung Galaxy S8 or S8 Plus (they can't be unlocked until you've paid off your contract), you can unlock any O2 phone - including iPhones - for free if you're on a pay monthly contract. PAYG customers have to pay £15.

What SIM card size do I need?


Let the retailer or network you're grabbing your SIM from know which size you need. Alternatively, many will now simply send out a triple SIM, so you'll get one of each size and you can simply insert the appropriate one in when you receive them.

How do I keep my old number?

There's a bit of work fo you to do here, but it isn't too tricky. It involves requesting a PAC - or Porting Authority Code - from your old network. They'll send you the code in a matter of a few days and you then give it to your new network who will do the rest. Here are the contact numbers to call to request your PAC:

  • EE 07953 966 250
  • O2 0344 8090202
  • 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

If you want to grab an unlimited data SIM above from a retailer, 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.


What contract length should I get?

You've got two options, basically. You can either sign up for a 12-month contract, or choose greater flexibility by signing up for a month-by-month plan. With Three, the tariff rate is slightly less if you go for the longer commitment. But if you're just biding your time before snapping up a great new phone deal, then it's worth paying a little extra to get the shorter term - that's where Smarty's offer can help, thanks to its 30-day contract length.

Do I need unlimited calls and texts as well?

The good thing about unlimited data is that it means you have other avenues to make calls and texts away from your network. For example, WhatsApp and Skype let you call and text for free over wi-fi or 4G. And Three even has its own Three inTouch app that specifically lets you take advantage of all that data for your chatting.

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The unlimited SIM only deals on this page are updated every day to make sure we have all the best deals and prices! If you're ready to go SIM only, then head back to the top of this page and use our tool to find the perfect plan...