Mundu Speak is a new VOIP software for Symbian S60 and Windows Mobile users that allows you to make and recieve mobile to mobile calls via GPRS/UMTS. The problem being you can make and recieve calls to and from users who have Mundu Speak installed on their mobile phones. You can also Send and receive unlimited instant text messages along with making calls
At a later stage, Mundu Speak users will get an interoperable Instant Messenger and be able to talk and conference with their friends on other popular voice messengers, landline phones and mobile phone subscribers worldwide at a low monthly cost.

There are three clients available- Symbian S60 v2, Windows Mobile PPC and a Java based client