Windows Mobile Smartphone users, those with non-touch screen phones, who like the VoIP communications of Skype can now use the service without a PC. IM+ for Skype is a software package for mobiles that lets you communicate via voice and text with other Skype or MySpace users. You can also use it to place low-cost calls to landlines and other mobiles. Use IM+ for Skype to send text messages and to chat with other Skype users or see who's on line. Texting over Skype can be cheaper than using your carrier's text function, though this will, of course, vary. The software runs on Windows Mobile 5 or 6 and requires an Internet-capable phone. It's $19.95.
Here is a list of compatible devices.