The 3G iPhone is maintaining consumer interest two months after it was launched, now racking up an estimated 27,000 sales per week, after a high of 50,000 per week in its first two weeks on sale, Mobile understands.

The Apple device is believed to be maintaining 27,000 sales per week through a sustained advertising campaign across TV, billboards and print.

It is believed to be hovering between a 4% and 6% share of the handset market, and even reaching ‘high single digits’ some weeks, according to a source close to the matter.

Despite the encouraging sales, O2 and Apple are keen to sustain the levels in the run-up to Christmas, with prepay taking the baton from contract.

Sales were hampered following the 11 July launch amid registration problems and stock shortages at both Apple and O2 which frustrated customers eager to get hold of the 3G device when it was first launched.

First-week sales of the 3G iPhone racked up around 50,000 units despite the systems faults, but those levels dropped to 32,000 after the first month.

O2 has put aside a major chunk of its acquisition budget to the 3G iPhone to demonstrate to Apple that it should keep the exclusivity for future Apple devices.

O2 unveiled the £350 price tag for the 8GB version, and £400 for 16GB last week.

The source added: ‘Prepay will undoubtedly give it a lift, but how much is difficult to say in the Christmas run-up. Will people want to spend so much in the current market conditions?’

A spokeswoman for O2 commented on the relationship with Apple earlier this week: ‘We have a strong relationship with Apple and they are pleased with the sales of the iPhone to date.’