On its official feed, O2 revealed that it would not be taking pre-orders and customers would have to go to one of the company's stores to get an iPhone 4S on 14 October.

"On launch day, you will not be able to upgrade online. You will have to get along to your local O2 store on the 14th October," the company said.

"Only existing O2 customers will have the ability to upgrade in store, on a first come, first served basis," it added.

Details of tariffs haven't yet been revealed, despite the fact that rival operators , have all released theirs and are all taking pre-orders as well.

Predictably, many O2 customers are unhappy and have expressed their discontent on Twitter.