SIM only contracts come in all shapes and sizes and given the combinations of data, minutes and texts there's a SIM deal for everyone.
The most important part of choosing your contract is deciding how much data you will use. Many customers are used to having a set amount of data with their previous contract so you can use that to choose the data you need. There's a huge variety in data packages, from 250MB all the way up to Unlimited Data so you can find the right amount for you.
The number of minutes avaiable with your contract can vary but most packages included Unlimited minutes as standard, especially if you're choosing from around 4GB of data upwards
SMS is even easier since most networks now included unlimited texts with all SIM only deals - gone are the days of counting your text messages. Since most people communicate with social media and messaging apps SMS usage is fairly low any way
One thing many people overlook when choosing a SIM contract is that there are actually two different lengths of SIM contract (usually).
12 Month SIM Contracts do what they say on the tin, your contract lasts for 12 months and you pay each month. Don't forget that when your contract ends that doesn't mean you stop paying. The time limit is just how long you have to keep paying for, you can switch at any time after the 12 months end.
30 Day SIM Contracts are slightly different because you can change your contract and even your network after 30 days. This more flexible option is great for people who want to change their contract regularly or know they don't need a SIM for a full year. Keep in mind that 30 day SIM contracts are usually slightly more expensive than the 12 month ones. Some networks only provide 30 day contracts also.
If you have a SIM contract and would like to change your data amount this is usually possible if you speak to your network provider, they can just amend your account and you will pay a new amount - They want to keep you happy so let them!
Many SIM contracts have parts which are Unlimited whilst there are usually some terms which apply to this, for most customers "Unlimited means Unlimited". Even for Unlimited data there are only restrictions for those using the SIM for commercial use.