Tesco has launched the cheapest mobile contract on the market, but it comes with a sting in the tail for mobile internet users.

The Sim-only deal, which costs £6 a month, provides 100 minutes of calling time (then, 20p per minute) and unlimited texts (see the Cheap Mobiles guide).

You are only tied to a one month contract but you won't get a new phone, so you'll need a handset that accepts Tesco Sim cards (see the Mobile Unlocking guide).

However, there is no inclusive internet allowance, meaning you'll pay a hefty £4 per megabyte, which could comfortably be used up in one browsing session.

iPhone warning

It means iPhone and other smartphone users should avoid this deal as many apps require the web (see the Cheap iPhones guide).

Daniel Lawrence, MoneySavingExpert.com consumer products analyst, says: "This is the runaway cheapest deals for texters, and is good for occasional talkers.

"However, the sting in the tail is the high data charges, so don't even consider this deal if you use the internet on your handset."

Research by Tesco Mobile shows 16 to 24-year-olds are the most prolific texters.

Lance Batchelor, Tesco Mobile chief, says: "This deal is ideal for any text addict who doesn't want to fork out a large amount each month.

"We've seen a big increase in Sim-only mobile tariffs."

Further reading/Key links

Slash mobile costs: Cheap Mobiles, Mobile Unlocking, Cheap iPhones, Sell Old Mobiles
Full details: Tesco Mobile website