STORY UPDATED: see below

Skype is now available for the iPhone – and will be coming to BlackBerry in May.

The VoIP app on the iPhone is intended to only work over Wi-Fi and not 3G. It will allow iPhone subscribers to use phone numbers in their existing iPhone address book – without the need for duplicate lists.

As always, it allows free calls between Skype users and charges for calls to landlines or mobiles.

The VoIP app allows iPhone subscribers to use the phone numbers in their existing iPhone address book – without the need for duplicate lists.

News of the VoIP client coming to the iPhone and Blackberry was first reported by Gigaom ahead of this week’s mobile-centric CTIA conference in Las Vegas.

The application for the BlackBerry platform will work in a similar fashion to that for the iPhone.

The iPhone and Blackberry apps are being seen as part of Skype’s efforts to expand beyond its PC stronghold.

Skype Chief Operating Officer Scott Durchslag said getting the app onto the iPhone was the top request from customers.

He said there was "pent-up demand" for the service on the Apple handset.

Skype has already been announced for Nokia and Android phones, as wel as handset operating Windows Mobile.

The service will also work on later versions of Apple’s latest iPod Touch device, which has Wi-Fi links but no cellular connection.

While Skype video is very popular with desktop customers, Durchslag said that the company is still considering whether it will offer video for the iPhone or other phones.

"We’re considering video carefully but we have a really high bar on the quality," and how the user interaction will work with other applications on iPhone, he said. "If we do it we will have to do it incredibly well."

Some other pieces of functionality are missing.

While Skype is certain its native client will provide superior audio quality – there is no need to route through another server and transcode audio – the app is missing text messaging, file transfers and integrated voice mail.

This will undoubtedly help multi-function apps like Fring and NimBuzz maintain a healthy presence on the iPhone, which famously doesn’t allow for multiple programs running concurrently.

UPDATE: Since being released on Tuesday it has emerged that Skype on iPhone does works over 3G, despite being intended only for use with WiFi.

Users report it working over the 3G data connection if the beta 3.0 firmware is being run.

Since VoIP over the 3G cellular is clearly forbidden in the SDK rules, it’s obviously due to a bug on 3.0 that it works.

This raises the question of how long it will be before Apple closes the hole?

But also, how did was the app "approved" and certified by for the App Store without first "testing" if Skype would work on the 3G connection?

Subscribe to our Newsletter