Windows (search results)

Nimbuzz
Cost: FREE

Nimbuzz is one of the most popular mobile messaging apps because it works on all platforms. You get free messaging (and phone calls) to any other Nimbuzz user wherever they are in the world.

Better still, by adding your social networking logins, such as Facebook, to your Nimbuzz account you can chat for free to all your social networking friends and contacts directly from Nimbuzz too.