Mobile operator 3 is offering a monthly contract that doesn't have a monthly charge.

The Sim Zero plan, which will be available form June 17, offers users the ability to make Skype-to-Skype calls and send instant messages (IMs) from their handsets for free. The mobile operator announced last month it was giving all customers the ability to make free Skype-to-Skype calls, providing they have a compatible handset.

Calls to other mobiles will be charged at 20p per minute with texts costing 10p each. Customers that sign up to the Sim Zero plan will also get a free voicemail service.

Users must sign up for a minimum term of one month, but after that they are free to cancel whenever they like and only have to provide 30 days notice.

"For customers who are fearful of commitment, Sim Zero has minimal ties. Customers can try us out and if they don't love being with us, they can leave with just one month's notice," said Andy Nuttall, head of pay monthly at 3.

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