TalkTalk's new unlimited SIM is the cheapest in the UK

Unlimited minutes, texts and data, it's the holy grail of phone contracts - and usually a rather pricey one - but not if you're a TalkTalk customer.

The broadband and TV provider has launched its new All-in SIM giving its customers unlimited everything for just £12 a month, on a 30 day rolling contract.

That's a fantastic sounding offer - but there are a few caveats. First up, it's not a 4G deal, so you'll have to make do with 3G data speeds. Tethering is also not supported, so you won't be able to tie your handset to a tablet or laptop and let them feed off your phone's internet.

Plus you have to be a TalkTalk broadband or TV customer to take advantage of the deal, you can't just pick up the All-in SIM with no other attachments to the company.

Still great value

TalkTalk promises 99% UK network coverage, as it currently uses Vodafone's network to deliver services to users, so you shouldn't struggle to find signal (unless you're in a Voda black spot).

If you're not fussed about 4G speeds then TalkTalk's All-in SIM is a great deal, as long as you don't mind signing up to another one of its services if you're not already a customer.