Owners of Windows Smartphones may now make phone calls using Skype for the first time, through the latest beta edition, 2.2, of the VoIP service for Windows Mobile devices.

Previously, the software was only compatible with Pocket PCs, of which a larger number devices are now compatible as well. Because of this update Skype said over 120 Windows Mobile PDAs and smartphones are now supported by the free calling service.

With Skype 2.2 for Windows Mobile users can make Skype-to-Skype calls or use SkypeOut to call regular landlines over a Wi-Fi or a high-speed 3G cellular connection. Users may also chat through text messaging.

Skype tends to be used over a WLAN connection, as most operators prefer customers not use the service over their cellular networks. Some mobile operators have even gone so far as to block Skype.

The exception is the 3 Group, which recently announced Skype support through iSkoot technology as part of larger program to encourage customers to use data services. With the 3 Group’s iSkoot-based Skype implementation, the client comes preloaded only on the Nokia N73 and Sony Ericsson W950 at present

According to Skype, users have so far downloaded 5 million of its Pocket PC clients.

In addition of Windows Smartphones and more Pocket PCs to its compatibility list, the beta of Skype for Windows Mobile 2.2 adds an enhanced today screen with presence status and event notification (missed calls, new chat messages and voicemails). There's also support now for regular HTTP or HTTPS proxies, and authenticating HTTPS/SSL and SOCKS5 proxies.

Per usual, Skype-to-Skype calls are free, while the SkypeOut service goes for an introductory rate of $14.95 per year plus 2.1 cents per minute when calling outside of the U.S. and Canada. It will go for $29.95 per year at the end of January.

internetnews reports the number of SkypeOut users tripled to 11.9 million this year, a 122 percent increase compared to 2005. Worldwide, Skype reports 136 million registered users.