Nimbuzz is an all-in-one voice and chat application for your phone. Regardless of whether you access Nimbuzz from mobile or PC, it allows you to: access several Instant Messaging platforms (AIM, MSN, etc.) simultaneously, make free calls to your GTalk or MSN contacts, make low cost (@ local rates) international calls, launch conference calls, send group messages and more. The Nimbuzz client available both as a downloadable client for mobile phones, as a web-based service, or as a Windows program.

Nimbuzz Features
Nimbuzz demo (mobile chat)
Nimbuzz demo (free international calling)
Check out Nimbuzz @ [www.nimbuzz.com]
Tags: client, free calling, IM, Mac/Win/Linux lists, Mobile Tools, voip | Categories: Chat / VoIP ¦ Conference ¦ VoIP-Calling / Chat
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[...] 5. Fring - Really cool mobile app that lets you place free calls or chat with anyone from your Skype, ICQ, Google Talk, MSN, Twitter, or SIP contacts. Video Demo. You can also get same stuff with Nimbuzz. [...]
i presonally prefer Papaya
http://www.getjar.com/products/16561/Papaya
http://www.papayamobile.com
with all the communication features, and you can play social games with friends