O2 claims it has already sold more iPhone 3GS handsets than it did on the launch day of the iPhone 3G.

O2 spokeswoman Emma Hart confirmed that the higher sales were not due to the registration issues that marred the launch of the iPhone 3G. She told Macworld: “Last year we had a slower processing time for the first hour, but by 10am we were up and running fine. We are confident we processed as many customer as we could that day.”

The mobile phone network described seeing 10 times higher than average footfall in its stores during the launch morning, leading it to anticipate selling 50 per cent more iPhone 3GS handsets than it did on launch day for the iPhone 3G.

Hart went on to confirm that the company was confident it would be able to meet demand for the iPhone 3GS. “We have been through the experience before so we are able to anticipate stock levels, and replenish them quickly.”

“We are delighted with the sales of iPhone 3GS, we will be refreshing stock in stores overnight for the weekend with a further delivery early next week,” added Hart.

Macworld visited the O2 store on London's Oxford Street earlier today and found that demand was steady – there was a 45-minute wait and the only customers being allowed into the store are those who are buying a new iPhone. Most people we saw said they were new to the iPhone, as opposed to paying for an upgrade. However, Hart confirmed that O2 had seen a mix of customers looking to upgrade existing iPhones and those new to the Apple mobile.

Hart suggested that existing O2 customers may have a perception that it is easier to upgrade their mobile by going straight to O2. “If a customer has an existing contract with O2 they may have the perception that it’s easier to upgrade with O2. They can come into the store and talk tariff options though. Maybe talking to O2 directly makes sense,” said Hart.

However, she was quick to add that she couldn’t comment for Apple.

One interesting observation is that the black iPhone 3GS is outselling the white version by 3:1. O2 also confirmed that over half its iPhone customers have already downloaded the iPhone 3.0 software.