Here is my Latest UI concept. This time i choose Windows Phone version. Nimbuzz launched a brand new version (1.0) for Windows Phone last Month but surprisingly it doesn't have some important features like VOIP,Group Chat..etc. The Concept here Based on version 1.2.0 which is not available yet.
So Lets Start with the 1st feature i have designed.you can see a home screen above.yes, since Windows Phone UI is based on live tiles,adding a home screen might look nice.so after the login,user will redirect to this home screen where user can select the option he want.N world tile and VOIP local call dialer tile are at the bottom.