Apple shares tumbled four per cent today after figures appeared to show worse than expected iPhone sales.

Exclusive operator AT&T said that it signed up 146,000 subscribers to the iPhone in the first two days, which is much lower than analysts had predicted. Some were expecting subscription rates of 500,000 within that time.

However the figures may be misleading, since they only cover activations and not actual phone sales.

"The difference [between sales and activations] is going to be what was sold on eBay or activations that did not happen immediately," Andy Hargreaves, an analyst at Pacific Crest, told Reuters. "There were some problems with activations but from what we heard it was minimal."

Hargreaves had predicted 400,000 activations by this time.

Further evidence about the long term popularity of the iPhone can be found in sales of the iPod, which did not sell as fast as predicted in the early days after launch but grew to be a worldwide phenomenon.

"Expectations were certainly high, but I am pleased to say that the iPhone has truly met them," said AT&T chief financial officer Rick Lindner during a conference call with analysts.