barablu is a new freeware software for Windows Mobile phones and Windows PC that allows you to make mobile to mobile calls via GPRS or WiFi.

Apart from making mobile to mobile and mobile to PC calls, it also offers the following functionality:

-conference calling: You can have a conference call with up to 49 barablu users on their Wi-Fi enabled mobiles - as well as Pocket PCs, PCs and even IP phones.
-chat: chat with other barablu users on mobile or PC
-video calling: stream video to other barablue users on mobile or PC
-file sharing & transfer: directly send files to other barablue users
-voicemail: allows you to recieve voicemails from others if you are busy

Download Links:

1) The PC version here
2) The Windows Mobile 5.0 version for Pocket PC here
3) The Windows Mobile 2003 version here