EE is the UK's biggest, most popular provider, offering (marginally) the best coverage. It's owned by BT and has everything from phones to SIMs and more.
One of the big four UK networks, Vodafone offers everything from SIM deals to mobile handsets, tablets, mobile broadband dongles and gadgets.
If you're a Sky broadband and/or TV customer, getting all your bills in one makes sense. Sky Mobile offers deals and a limited range of handsets.
The mobile area of Virgin Media, Virgin Mobile offers some fantastic deals on SIMs and handsets, especially if you're a Virgin Media customer.
Three is one of the UK's four main network providers and offers everything under the sun, from handsets to SIMs to tablets and more.
Although BT owns EE, it also has its own brand network: BT Mobile. It's an especially good choice if you're already a BT broadband and phone customer.
You won't find any handsets available on Plusnet Mobile, but if you're happy with the one you've got, it offers some of the cheapest SIMs around.
Unlike Tesco Mobile – the other supermarket-come-mobile provider – you'll only find SIM deals with ASDA Mobile. Some of the cheapest around, in fact.
Still relatively young, iD Mobile is the in-house mobile phone and SIM provider of High Street brand the Carphone Warehouse.
Another of the UK's four main network providers, O2 offers anything you could possibly want: Handsets, SIMs, pay-as-you go, tablets, you name it.
With a customer service and support network comprising its own customers, giffgaff can offer deals on SIMs and handsets that are cheaper than most.
VOXI Mobile is a Vodafone brand aimed at a younger audience, offering free social media data as standard with all of its SIM plans.
SMARTY is owned and run by Three. Its reasons for existing are simplicity and flexibility – it offers only three plans, all on rolling 30-day contracts.
As well as supermarkets, Tesco offers one of the best value mobile services in the UK, with a wide range of handsets and SIMs for all budgets.
For those with a big heart, The People's Operator aims to give a slice of your monthly fees to charity. It offers only SIMs, though – no handsets.
The Phone Co-op, like the co-op proper is co-operatively owned and run by its members. It offers a good range of budget SIMs with no hidden charges.
Lebara Mobile specialises in offering SIMs to migrants and visitors to the UK who wish to stay in touch with their friends and relatives abroad.