Simple Guide To SIM Cards

Sim Card deals

With pay monthly, pay as you go sims, 30-day sims and more available nowadays, it can be hard to figure out which SIM is right for you. Everyone's needs are different. In this guide, we’ll be showing you the difference between SIMs, their benefits (and drawbacks) as well as pointing out some details you won’t want to ignore, next time you are on the hunt for your next SIM plan.

Pay Monthly

Pay monthly SIMs are one of the most common types of SIM these days. Offering you an allowance of minutes, texts, data and sometimes other benefits for a flat monthly cost. These are typically cheaper than mobile contracts as you are paying for the service plan only, without the additional cost of a handset. These are available on all the major networks and are usually on a term basis, meaning you have to maintain the plan for a set amount of months. The plans offered usually range from 30-day contracts, giving you flexibility should the SIM not suit, or you only need it for a short period of time, all the way through to 24-month contracts, meaning you’ll need to pay for the service for the duration.

Once you have signed up, it’s as simple as receiving the new SIM card, putting it into your phone, and then you can begin to use your allowance of minutes, texts, data and other add-ons.

Sim card and phone
Source: Silvie Lindemann / Pexels.


Pay as you go SIMs, or PAYG as they are commonly referred to, allow you to top up your sim with credit, and then use your credit in exchange for minutes, texts and data, making sure you can only use what you can afford, these are a great option for younger members in the family, who want a phone, but you want to ensure spending can be controlled, or budgeted. This also allows them to top up their credit freely when they can, and as there is no contract tie-in, these provide greater flexibility for those that perhaps only need to use it sporadically.

What size SIM do I need?

So, you’ve received your SIM card in the post, or perhaps you are in the process of ordering and realise you have no idea what size of SIM card your phone uses. Most SIM providers offer a single SIM that can be made to fit all phones called a 3-in-1, but if this isn’t the case, please see below for the different sizes you may come across.

  • Standard (25 x 15mm)

    This is the largest type of SIM, and the one we normally see advertised. Despite its presence in ads, this is now the least used SIM, considering its size, modern devices try to save space wherever possible, and this size of SIM is quite large in comparison, and has therefore been gradually phased out, however an older or larger phone may still support it.

  • Micro (15 x 12 mm)

    Devices started to get smaller, and therefore so did the SIM card. Whilst the Micro was an improvement to the standard size, it has been superseded by the Nano. 

  • Nano (12.3 x 8.8mm)

    The smallest SIM available on the market, and without doubt the most commonly used these days. If you’ve bought your handset recently, it is likely compatible with a Nano SIM.

  • eSim

    You may also come across an eSIM. These are electronic SIMs which are supported by the latest devices, giving the same functionality as a sim, but no physical SIM card is needed. 

How do I change my SIM card?

Changing the SIM card in your device, such as an iPhone, is a relatively quick and easy process:

How do I compare SIM plans?

Comparing SIM plans is a relatively easy process. Most SIM plans offer 3 standard benefits of included minutes, texts, and data. You’ll be able to compare competing SIMs allowance and pricing against each other, but there’s some other important considerations to make:

  • Allowance - what do I need?

    Perhaps you are comparing SIM plans, and notice a plan with double the allowance, or even unlimited; for an extra £2 a month. Tempted? It’s worth considering what you will actually use, as you could find yourself paying extra for an allowance you’ll never use, and £2 over a 24-month term, for example, is an additional £48 you’d be paying. It’s important to consider how much you will use most months, and try to find a suitable plan which covers this. 

  • Additional benefits

    Some networks offer additional reward schemes for customers, bringing additional value to your plan. One example of this is the new Three+ app, which currently offers reduced price cinema tickets. If you are a regular cinema-goer, and would avail of this recurring discount, it’s worth considering this into your decision on your SIM plan. 

  • Cost

    A somewhat obvious consideration, but it’s worth shopping around for the allowance you need, as various networks will have the plan you need at different price points. It’s also worth considering the terms of these contracts. 24 months is a long tie-in, but it may come with a discount on the monthly charge as a reward for your commitment, saving you more over the longer term.

  • Network Coverage

    Most networks do a pretty great job of ensuring coverage across the majority of the UK, but we all know the frustration of sitting in a place with poor or no coverage. If you are spending a significant amount of time in certain places such as work / home, and you have no experience with the network, it is definitely recommended to check coverage to ensure you will be happy with the level of service. Most networks have an online tool which will allow you to check this, but they are never 100% accurate, and that should be considered if you are on the fence with switching providers. Links to coverage checkers for the major networks are below:

Benefits of a SIM-only plan

If you have a mobile contract that’s coming to an end, a SIM-only plan is the perfect way of continuing to use your device, and save money as you will no longer be obliged to pay for the phone element of your contract as that has now been paid off. 

Or perhaps you are able to buy a phone outright, and a SIM-only plan is the perfect way to keep costs down, as combining a SIM-only plan with a SIM-free phone is always cheaper than paying for a mobile contract. This also allows you to avoid any lengthy contracts, giving you more flexibility. 

SIM-only plans also typically have lower credit check requirements, as the total amount of the contract is lower. This should help anyone that has perhaps struggled to get a mobile contract in the past, and should you be successful, continuing to pay your SIM-only plan will benefit your credit score in the long run.

Money Saving Tips

You’ll want to keep these points in mind the next time you are looking for a SIM-only plan:

  1. Check your current provider for offers

    If you are at the end of your mobile contract, speak to your current network provider who may be able to offer you a discounted plan in the hopes of retaining you as a customer. Typically, this is a cheaper avenue for the business, so they are incentivised to keep you as a customer. Speak to their Customer Services team, or retention team, and explain your circumstances for them to advise what they can offer, but do not be afraid to walk away for a better deal elsewhere.

  2. Longer commitment = better savings

    Typically networks will offer a more attractive price point on longer-term plans. They want to retain you as a customer for longer, and will attract you with lower prices with a longer tie-in. Provided you are confident your needs won’t change over the longer term, then this is an easy way to save even more money.

  3. Set a monthly spending cap

    Perhaps you have decided to reduce the allowance of your plan in favour of a cheaper monthly cost, but are concerned that you may reach your max allowance or even go over it. By setting a monthly spending cap, the network will not allow you to spend over and above the cap, protecting you from unexpected high bills.

  4. Move away from the big networks, and consider a NVMO

    NVMO’s or Mobile Virtual Network Operators, are smaller providers who piggyback off one of the larger networks to provide you phone service. A good example of this is SMARTY, who operate on the Three network, giving you access at a lower cost. These smaller operators typically have more flexible plans, as well as stripping down any additional add-ons to provide you a more basic phone service at a much lower cost. If you don’t need the bells and whistles, then why pay for them? 

  5. Make sure your phone is unlocked

    Sometimes mobile plans will offer you a phone included in the monthly cost, but this handset may be restricted and locked to the network who provided it. If you plan to switch to a SIM-only from another network, you will need to ensure that your phone is unlocked and will support it. Typically, most providers are happy to do this at no additional cost at the end of your contract as you have paid for the device, however, please check with your network that this is the case.


How do I switch to a SIM-only plan?

If you are already in a mobile contract, you’ll need to wait for this to conclude before you consider using another SIM plan. Otherwise, you may end up paying for both plans until your original plan has finished, or even worse, ending your contract early which may result in early termination fees. When switching, you’ll need to let your current provider know.

How can I tell my phone is unlocked?

Is Pay As You Go cheaper than Pay Monthly?

Can the monthly cost of my SIM plan change?