Have you ever wondered what a SIM card is and how it actually works? That little bit of plastic that unlocks your mobile phone and allows you to connect with the world? Here we look at how a SIM card (or Subscriber Identity Module, to use its full name) works, as well as a brief history of its evolution.
How Do SIM Cards Work?
Back in the early days of digital technology, when mobile phones were analogue, it was relatively easy to hack into a conversation between two people. That was until around 1992 when the first ‘GSM’ (Global System for Mobile communications) phones and SIM cards were introduced, and we entered into the digital age.
The SIM is part of a European telecommunication standard separating mobile phones from mobile networks. SIM cards contain a small microchip that has a unique ID (the IMSI, or International Mobile Subscriber Identity) that your network operator uses to identify you. It contains your phone number, and has its own allocated memory for storing your address book and text messages. This means you can swap your SIM card between mobile phones (if compatible) and have your personal information available on that phone.
When a telephone call is made over the mobile network, GSM technology converts the voices into encrypted digital data before sending it over the mobile airwaves. The SIM card stores the password, or “key”, needed to decrypt the data.
Are SIM Cards Universal?
SIM cards are universal in the respect that they will fit any mobile device that uses that particular sized SIM card. Although they might fit, if you use a SIM from one network and expect it to work in a phone locked to another network, then it won’t operate. But that is the fault of the mobile itself and not the SIM.
What Shapes and Size Do SIM Cards Come In?
When SIM cards first appeared they were quite big, about the size of a credit card. This was OK for the brick-sized mobile phones originally available to consumers, but as technology advanced and mobile phones became increasingly smaller, it wasn’t long before SIM cards were too big. A compromise was reached by creating thumbnail SIMs within standard SIMs, which could be snapped out to fit neatly inside newer mobile phone models.
This worked well for many years, but with the advent of smaller and skinnier smartphones, internal space became a design issue that needed solving. The solution designers came up with was a Micro-SIM, which is almost identical to a standard SIM but with less plastic. To begin with Micro-SIM cards were not widely used, but after Apple adopted a Micro-SIM for the iPhone 4, other manufacturers soon followed suit.
Not surprisingly, manufacturers haven’t stopped at a Micro-SIM and in 2012 Apple introduced an even smaller SIM. The Nano-SIM is essentially just a tiny microchip without the surrounding plastic. It was first used in the iPhone 5, but most of the latest handsets have ditched the Micro-SIM in favour of a Nano-SIM.
Do I Need a SIM Card?
Mobile phones won’t work without a SIM card. The SIM connects the phone to the mobile and data network, so if your SIM is missing, your phone will be pretty useless. However, the one thing you can do with a SIM-free mobile phone is dial 999 in an emergency.
Why Mobile SIMs Don’t Work in Tablets
Tablets are not dissimilar to smartphones in that you can access data networks and install apps. However, smartphone SIMs do not normally work in tablets because they are designed for voice and data, whereas a tablet SIM can only provide access to a data network such as 3G or 4G. SIMs can be swapped over, but will almost certainly not work because the network provider will block a mobile SIM if it is not installed in the correct device. So if you want to make calls on your tablet, try installing an app such as Skype.
The Curse of the Blocked SIM
SIM cards have in-built security features to protect the device they are installed in from theft. Your SIM can be locked if your mobile phone is lost or stolen – a quick call to your network provider will prevent unauthorised use of the mobile and save you from a huge bill. It is also possible to inadvertently block a mobile phone by applying a SIM lock and then keying in the wrong PIN three times. But don’t worry if this happens to you because it can easily be unlocked with a call to your network provider (although they may charge you).
As you can see, the humble SIM is a pretty amazing piece of technology. It is also very useful because you can switch to a new mobile without the hassle of retyping your contact address book all over again.You’ve probably heard of the term SIM only contract before, but what does it mean? If you don’t want to get a new handset or Pay and Go, SIM only contracts are the answer. We’ve answered some of the most commonly asked questions about SIM only contracts to help you understand what they are and how they work.
What is a SIM Only Contract?
SIM only contracts are like a pay monthly contract, however there is no mobile phone handset included with the deal – it’s just the SIM card. For this reason, they are usually much cheaper than a regular mobile phone contract, and they don’t last as long – most SIM only contracts have the option of being a 12 month contract or even just 30 days meaning that you’re not tied in.
What is the difference between a SIM only and long term contract?
Long term contracts tend to last for 24 months, and you’ll get a handset included – either free of charge or for an upfront fee, depending on the contract and handset that you choose. With a long term contract, you will need to commit to paying the monthly amount for 24 months, and if you want to change your phone handset or price plan during the 24 month term you’ll most likely be charged a fee.
SIM only contracts are different – there is no handset included, so you will either need to buy your own handset or use one that you currently have. SIM only contracts are a great option if you love your current handset and don’t want to change it, or if you’re waiting for a certain handset model to be released before you get it on contract.
SIM only contracts also don’t last as long as a regular contract – the most you’ll be tied into a SIM only contract for is either 12 or 18 months. Some networks, such as Vodafone, also offer the option to upgrade to a regular contract with a phone 3 months into your 12 month contract without a fee – great for those with poor credit or if you’ve got a few months to wait before a phone that you like is released.
You can also get SIM only contracts on 30 day deals – these are a great option for those who want all the benefits of a monthly phone contract without the commitment.
What is the difference between SIM only and a Pay as You Go SIM?
With a Pay as You Go SIM, the user has to ‘top-up’ the phone with credit whenever they run low. Although some Pay as You Go deals offer bundles of minutes, texts and data, you’re usually charged per minute, text or MB and this is deducted from the credit that’s available on your phone. Pay as You Go can be quite expensive for regular phone users – especially those who like to browse on their phone.
SIM only contracts don’t require you to top up – you pay a monthly regular payment by direct debit and your tariff allowance is renewed each month. They work in the same way as a regular phone contract, although there is no handset included.
What is the difference between 30 Day SIM only and 12 Month SIM only?
With a 12 month SIM only plan, you will need to sign a contract committing to pay the set amount each month for 12 months. Most networks offer 12 month SIM only plans at a reduced price as a reward for choosing to be with that network for 12 months.
However, with a 30 day SIM only, there is no contract – meaning that you can cancel or change your plan at any time without needing to pay a fee. 30 day SIM only contracts also tend to have more lenient credit checks, meaning that they’re a great option for people looking to build their credit rating in order to get a regular contract.
Which networks offer SIM Only Deals?
Almost all of the main UK networks offer a range of 30 day and 12 month SIM only deals, including EE, Three, Vodafone, O2, BT Mobile, Virgin Mobile, Tesco Mobile, TPO, iD, and Mobile by Sainsbury’s.
What are the benefits of SIM only?
One of the main benefits of SIM only is that it’s cheap – there’s no need to cover the cost of a new handset. They’re also great for people who don’t want to be tied into a long contract or don’t want to commit to a contract at all. Because 30 day SIM only contracts don’t require a strict credit check, they’re also beneficial to people who have poor credit and want a phone contract.
So, now you know all about SIM only contracts! If it seems like something you would benefit from, we’re sure you’ll find a great deal – there are loads to choose from!