Best mobile phone deals SIM only: the ultimate guide with the latest offers

If you don’t want to be locked into a lengthy contract, and you’ve already got a phone, these best mobile phone deals SIM only could be just the ticket. 

SIM-only deals are ideal for anyone who doesn’t need or want a new phone, and who would like flexibility rather than being tied to one particular provider for months or years at a time.

In this guide, we explain everything you need to know about SIM-only deals, as well as providing a shortlist of some of the best deals currently available. 

 What is a SIM-only deal?  

As the name suggests, with a SIM-only deal, you only get a SIM card, and no handset. SIM is an acronym for ‘Subscriber Identity Module’ and it’s basically the small bit of plastic which slots into the back of your phone. It’s the SIM that allows you to connect to your network so you can make calls and send text messages. 

SIMs also hold all the information you need on them, such as emails, contacts and so you, and are transferable, so you can move yours over to another handset at any point if you want to, provided it isn’t locked to another network. 

How does a SIM-only deal work? 

There are two main types of SIM-only deal – pay monthly and pay as you go. With a pay monthly SIM-only deal, you’ll sign up to a rolling 30-day contract and will get an allowance for calls, texts and data to use each month. If you want to end the contract at any time, you simply give 30 days’ notice. Some SIM-only deals allow you to commit to a 12-month contract if you’re comfortable being tied in for a longer period.

Pay as go SIM only deals require you to top up your phone with credit as and when you need it, so you’re not tied into a contract at all. Once you’ve found and applied for the SIM-only deal you want and you receive the SIM from the network provider you’ve chosen, you simply insert it into your telephone, following the instructions you will have been provided with, and you should be good to go.  

 Why get a SIM-only deal?  

The biggest advantage of a SIM-only deal is that they are much cheaper than other mobile deals because you’re not paying for a handset. The only cost is for the data, texts and minutes you’ll use. 

Another benefit is that SIM-only deals are more flexible than other types of mobile deal - you won’t be locked into a lengthy contract, so if you want to switch providers, you’ll usually only have to give 30 days’ notice. 

(MORE: How to save money on your mobile phone deal)

SIM-only need-to-knows 

Here’s an at-a-glance guide to some of the essentials you need to know about SIM-only deals.

What does a SIM card do and what’s stored on one?

A SIM card is essentially a computer chip which is used to store information such as your contacts, emails, photos and messages. It enables you to connect to your network provider so you can make calls and send texts and so one. Without a SIM you wouldn’t be able to use your phone. 

How much data do you need?

The amount of data you’ll need from your SIM-only deal depends on how you use your phone. For example, if you regularly download large files on your phone, you’ll need more data than someone who just uses their phone to send texts and make calls. Check previous bills to see how much data you tend to use each month, but as a general rule, most people typically use up to around 3GB a month.

What contract lengths are available?

SIM-only deals typically run on a 30-day rolling contract, providing you with flexibility if you decide you want to switch to a different network. However, it is usually possible to sign up for a 12-month contract if you want to. 

How to switch SIM-only deals

If you want to move to a different SIM-only deal, you’ll need to wait until your current contract finishes. Most contracts only run for 30 days so you shouldn’t have to wait long. If you want to keep the same number when you move, you’ll need to request what’s known as a PAC code (Porting Authorisation Code) from your existing provider which you can do by texting PAC to 65075. When you’ve got your PAC code, you’ll need to get in touch with the provider you’re joining and give them the code so they can then arrange the switch on your behalf.

Will my phone be locked to a network?

If you have a SIM-only deal, then it’s only the SIM that is locked to the network and not the phone handset itself. A locked phone is a handset which will only accept a SIM card from a particular network. From December 2021, mobile companies will be banned from selling phones which only work with their network.

(MORE: EE versus O2: which is better?)

How to unlock a smartphone

If you want to unlock a smart phone that’s locked to a particular network, you’ll need to contact the network provider and give them your IMEI number, which essentially identifies your phone. You can find this in the Settings section of either your iPhone or Android phone under the ‘About’ or ‘About device’ heading. Different networks have different approaches to unlocking phones, so you’ll need to check with them how long the process will take and whether there are any costs involved. 

SIM networks and piggybacking

Even though there are only four main networks (Vodafone, EE, Three and O2) several other providers piggyback on their signals, often offering competitive deals. This means that even if you can only get good coverage in your area from one particular provider, you should still be able to pick from a wide choice of deals when you include piggyback providers. These providers include Smarty (Three), GiffGaff and Tesco Mobile (O2), Plusnet and BT Mobile (EE) and Voxi (Vodafone).

Best SIM-only deals, up to 3GB of data 

Current best SIM-only deals include Lebara’s £5 a month deal, which comes with 1000 UK texts, 1000 UK minutes of calls and 2GB of data. Lebara uses the Vodafone network.

ID’s SIM Only deal also costs £5 a month, and comes with 1GB of data and unlimited minutes and texts.

Alternatively, Talk Mobile’s SIM-only 3GB deal costs £7 a month and includes unlimited calls and texts.

Our choice: Lebara’s deal comes with 100 international minutes of calls to 41 countries which we think gives it the edge.

Best SIM-only deals, 4GB of data up to 9GB of data – plus what we’d choose 

Smarty, which piggybacks the Three network, is offering a 4GB SIM-only deal for £6 a month, which comes with unlimited calls and texts. 

If you think you’ll need more data iD’s SIM-only deal provides 6GB of data and unlimited minutes and texts for £7 a month. 

For an extra £3 a month, at a cost of £10 a month, you can get 8GB of data with GiffGaff’s SIM-only deal, which again comes with unlimited minutes and texts.

Our choice: We like iD’s £7 a month SIM-only deal. It provides plenty of data and unlimited calls and texts at a competitive price.

Best SIM-only deals, 10GB to unlimited data – plus what we’d choose 

Smarty offers a SIM-only deal providing a whopping 30GB of data and unlimited minutes and texts at a cost of just £10 a month.

For the same price, you can get 10GB of data from Lebara, although the cost falls to £5 for the first month for new customers. This deal comes with unlimited calls and texts and 100 international minutes of calls.

If you think you’ll need unlimited data, then Smarty also offers a SIM-only deal costing £18 a month which provides unlimited data, minutes and texts.

Our choice: If you’re a heavy phone user, Smarty’s £10 a month deal provides a generous 30GB of data and you don’t have to worry about exceeding any call or text limits either.