If you're audio sounds great for a network game and crappy for a phone call (to the same person you are playing a game with), its because some one (your ISP, your VoIP software, the other parties ISP, or VoIP software, or any network hop in the middle), is intentionally choosing poor quality codecs for you to lower your bandwidth utilization.
I've heard directly of novice VoIP engineers unintentionally taking out corporate networks trying to "help" improve audio quality, by picking a higher quality codec. It worked great when they tested phone calls in the middle of the night maintenance window. It really sucked the next day when packets started colliding. Crappy sounding codecs sound a heck of a lot better than 50% packet loss.
I've heard directly of novice VoIP engineers unintentionally taking out corporate networks trying to "help" improve audio quality, by picking a higher quality codec. It worked great when they tested phone calls in the middle of the night maintenance window. It really sucked the next day when packets started colliding. Crappy sounding codecs sound a heck of a lot better than 50% packet loss.