Earlier we have posted about iBlueTooth Call tweak which also allows two way voice chat on iPhone and iPod touch but the problem is it works over BlueTooth, so within short range you can make voice chat. Using NetVoice tweak you can solve this problem and you can make voice chat over WiFi.
NetVoice is available in Cydia under ModMyI repository. You will need to have a jailbroken iPhone and iPod touch to install this tweak. If you don’t have jailbroken iPhone and iPod touch then you can follow the step by step instructions posted here to jailbreak your iPhone and iPod touch on iOS 4.2.1 with Redsn0w.