O2 and The Carphone Warehouse have both confirmed that stores have sold out of the 8GB iPhone, which was discounted by £100 to £169 last month.
Apple stores, which did not discount the device, still have the 8GB version in stock. The 16GB iPhone at £329 also remains available.
An O2 spokeswoman said: “We have been delighted with the response to our iPhone price promotion which has surpassed our expectations.
“Owing to this success we are currently out of stock of the 8GB iPhone. Customers keen to get the iPhone experience can purchase the 16GB iPhone at the standard price through O2 channels.”
Both O2 and Carphone said they were “reviewing stock options”, although the national press has reported that stocks would not be replenished ahead of the launch of an updated version of the device this summer.