

Fring is actually pretty cool. It's a thin client that allows you to talk & IM via your handset's Internet connection to other mobile phones and PC-based services such as Skype, Google Talk, MSN Messenger, SIP and Twitter for free. It also unifies all of your various contacts across all of these IM/VoIP networks so you can use a single app to view presence and initiate chat sessions or voice calls. Alas, no video yet. Though I haven't seen a good mobile videoconferencing app yet, so can't fault fring for that one. Video is actually pretty processor intensive and most mobile phones just don't have the horsepower.
In any event, fring can be downloaded into your handset via SMS received from another fringster or from their download page.
Right now you can only get the Nokia version, but the Windows Mobile version is coming (soon). Stay tuned!