O2 has warned customers that the iPhone 3G will be in short supply for some time to come.

The operator posted a notice on its site stating that the Apple handset will face shortages " for the foreseeable future".

O2 said that it is receiving weekly shipments of the handsets from Apple, and will continue to do so. But the iPhone 3G is in such demand that the device will be sold only in O2's retail outlets.

"We will continue to sell the iPhone 3G on a first come, first served basis to be fair to all customers," the company said.

"We are confident that all customers who want an iPhone 3G will get one by the end of the summer."

The retail-only policy will also apply to the iPhone upgrade programme which lets users trade in the first-generation iPhone for the new handset in exchange for an extended commitment on their contract.

iPhone buyers in the UK can also obtain the handset from Carphone Warehouse and Apple retail stores.

O2's struggles are only a small part of a worldwide iPhone 3G shortage. US carrier AT&T has warned of similar problems, and currently estimates that customers are waiting two weeks for an order to be processed.

Analysts have predicted that the shortage could last well into August.