Wadja (m.wadja.com) Is a mobile focused social network that has been around for about a year. It's very mobile centric, there is a desktop version of Wadja but you never really need to go there, everything can be done from the mobile web site.
Wadja has the usual social networking features of profiles, friends, content (music, video, pictures) sharing and chat. The thing that sets Wadja apart is the ability to send free SMS text messages to any number in the world. Of course the messages are only free if you have an unlimited data plan or send them from your PC. Wadja is based in Greece so sending text messages to numbers in other countries can be a little hit or miss as it depends there being an SMS-interconnect agreement between your carrier and whatever service Wadja is using. I never received any of the messages I sent from Wadja to my Boost phone on the Nextel network for example.