Fring
Fring is considered to be the most advanced vide-calling solution on the mobile platform. They have now launched group video-calling for Google Android smartphones, Nokia and iOS devices with support for up to four-way video calling functionality.
Fring was the first ever video-calling solution to offer free group video-conferencing and in recent updates, it has also offered free unlimited voice calls to other Fring users without any purchase of credits or tariff plans.