Skype has launched a beta version of its VoIP client for 50 models of mobile phone - but don't expect free calls, as this VoIP isn't all that it appears.
Skype has been available on special handsets from 3 for a while, but the service isn't really VoIP: it uses normal GSM for the wireless part of the call, then switches to VoIP at a Skype gateway for transmission over the internet. The new client works in exactly the same way, only without the accompanying operator tariffs.
With the 3 service you can make free calls to other Skype users, but Skype can't provide that with other network operators, so calls using the mobile Skype client will cost you the price of a local mobile call. Skype will also charge you for calling your mobile when you receive a call to your Skype number, and if you're roaming you'll end up paying both ends of the roaming charge.
So for calls there are probably cheaper alternatives, but the client also integrates with Skype messaging and presence servers, so you can use instant messaging and see if your contacts are logged on. Skype is careful to warn you that leaving yourself logged on could end up being expensive, though most usage should fall within the fair-use limits.
What's hard to understand is why it's taken Skype so long to do this. IM+, from Shape Services, has been offering the same capabilities for quite a while, and with Fring users can even make (genuinely) VoIP calls for free - though that's better restricted to when Wi-Fi is available. Fring is still lacking a business model, so might not be around forever, but without a genuine VoIP client Skype is in danger of losing customers to Truphone and its ilk.
Skype has claimed formidable technical challenges prevented the client existing earlier, but it seems more likely by launching a Java client on a range of handsets Skype can make some money out of existing users rather than launching, say, a Symbian client which would allow even more people to make free calls using Skype's infrastructure. ®