VOIP/EDGE Services through Symbian Phones?

Phones being released today are equipped with a new function called EDGE or more technically known as VOIP (Voice over IP.) This is a service which lets you talk over the internet through GPRS. The phone quality is slightly decreased and it is only availible in a few countries to this date. It should be fully possible to use any other symbian phone with the right software. It is possible to send video over GPRS so shouldnt audio be the same? Why is it nessecary for a specific function?

P.