Skype has released a Java client for mobile phones, compatible with S60 and UIQ devices. While the application looks like a "normal" Skype client known from PC or Windows Mobile, it is not a true VoIP solution as it uses the mobile network (rather than the Internet) to make and receive calls. This means that in addition to your Skype credit, you will also be charged by your network operator for a local call. Call quality is not that great, either, but it's just a beta version so things may get better. To try it yourself, visit http://www.skype.com/m.