Check out the iSkootDuo solution which enables dual mode phones support GSM/CDMA and Wi-Fi networks to connect to a number of VoIP services. So now enjoy connectivity with a number of services such as AIM, GoogleTalk, MSN Messenger, Skype and Yahoo Messenger.

It is a Java based thin client application which operates with a network server. You can download the software from their website. This is the only technology which enables VoIP over three different network connections. i.e. Wi-Fi, 3G/GPRS data, and GSM/CDMA

As of now there just a few dual mode phones which support it. Nokia E series phone gel with this software.