02 is cutting the cost of its iPhone tariffs just two months after its launch in the UK, stoking speculation that sales have been worse than expected.

The mobile phone company, which is Apple’s exclusive network partner, today announced new tariffs offering customers signing up for the basic £35 a month iPhone package, three times more free minutes and more than double the number of free texts than at present.

The iPhone £45 a month rate will now include 1,200 free call minutes instead of 600 minutes.

Existing customers will be switched to the new tariffs next month.

The handset price remains unchanged at £269.

To own an iPhone in Britain, customers must sign up to a contract costing £35-£55 a month with O2 for a minimum of 18 months, on top of buying the handset. That puts a basic price tag on the phone of at least £899 over 18 months.

The iPhone — a combined mobile phone, internet surfer and iPod music player — was launched in the UK in November.

Since the roll-out, O2 has repeatedly declined to publish exact customer numbers and anecdotal evidence from stores has raised speculation that the phone has not been the sell-out success that was expected.

However, Sally Cowdry, the marketing director of O2 UK, today insisted that the phone was “our fastest ever selling device".

In the US Apple endured customer wrath when it cut the price of the phone by 33 per cent only 68 days after its launch.

The consumer electronics group was compelled to offer customers who bought the gadget before the price cut a $100 credit note to spend in Apple stores with those who bought it in the 14 days before the price cut offered a full refund.

That cut also stoked investor speculation that sales were not living up to expectations.

Last week, Apple shares sank more than 10 per cent following first-quarter results which included muted guidance for the next quarter.

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