The Vonage Mobile soft client announced last week uses Google’s iSAC codec for HD voice. No G.722 on the menu.
No other detail (i.e. why, future codecs) was given In the brief answer from a Vonage PR spokesperson.
Vonage Mobile currently runs on iThings and Android devices, and delivers free HD voice calling between clients on IP wireless data network (3G, 4G, and Wi-Fi).