Skype has released a beta version its a software client that allows Windows Mobile smart phones to access the company's VoIP service over Wi-Fi connections.

Previous versions of the software were compatible with Windows Pocket PC devices but the beta of Skype 2.2 now works on 120 different devices, Skype said. Users in range of a free Wi-Fi network can make free VoIP calls to other Skype customers. Users can also pay via their SkypeIn and SkypeOut accounts to receive and make calls to landline phones.

New features in Skype 2.2 for Windows Mobile include an enhanced screen with presence status and notification of events such as missed calls and voicemails. The client also now supports secure connections including HTTPS, HTTPS/SSL and SOCKS5 proxies.

Skype promotes the use of its mobile client over Wi-Fi, not over cellular networks. Mobile operators have largely resisted Skype and some have even blocked the service because it can compete with their own voice offerings. But operators would have trouble blocking Skype calls over Wi-Fi networks, which they typically don't control.

Last month, 3 Group broke from its competitors and introduced a new data offering that enables customers to make and receive Skype calls over its 3G network. The service is initially available only on a single Nokia phone model and is supported via iSkoot, a company offering software that enables Skype on mobile phones.

In October, Eric Lagier, Skype's head of mobile development, said the company would introduce a client that would run on Symbian phones by the end of the year. Fans of Symbian, the most popular smart phone operating system, are still eagerly awaiting the much-delayed Skype client.