O2 is rolling out a much improved contract deal for iPhone users, offering more text messages and a higher call allowance for users on existing tariffs.

The move is part of an overall improvement in the network's offering for all its mobile phone customers. The company is introducing six new and simpler tariffs and introducing free voicemail for its new and existing customers from 1 February.

iPhone users on the cheapest (£35) tariff will now enjoy three times the call allowance (now 600 minutes) and be able to send 500 SMS messages (up 300) as part of the new deal.

The £45/month iPhone contract will now enjoy the same call/text allowance as formerly given customers paying £55 per month: 1,200 minutes and 500 texts per month.

And iPhone users on the top £55/month contract will either receive a £10 discount from their bill, or the chance to join £75/month contract, which offers 3,000 minutes of calling and 500 texts under the monthly deal.

O2 continues to offer an 18-month minimum contract on the iPhone, but the newly improved tariffs may well stimulate a fresh surge in sales of the device, as the original deal offered has been widely criticised for being too lean.