UK mobile operator O2 has warned its existing and potential customers that it expects the iPhone 3G to be in short supply when the device launches July 11.

The company sent out an advisory to all those that had pre registered their interest in the Apple device, saying that it does “expect demand for the iPhone 3G to be very high, so orders will be processed on a first come, first served basis.”

Orders will also be limited to one iPhone 3G per customer, presumably to keep a lid on the grey market, or those seeking to sell the device on.

Last week, the operator inadvertently revealed that the prepay version of the 3G Apple device will retail for £299.99 in the 8GB flavour, while the 16GB version will go for £359.99 without a contract.

In a bold move however, O2 is giving prepay users free, unlimited wifi and data access for six months, which is something of a first. After the first six months is up, users can continue to buy unlimited wifi and data access for £10 per month.

O2 UK is also expected to open its high street stores at 7am on July 11, to accommodate the expected rush of rabid Apple fans.