Mic works fine in my (360) version. That said, I have never used the game channel for chat, only the party chat. Near as I can tell, all Xbox live games work on a similar principle. The VOIP functionality is handled seperately from the game itself. This would explain, for example, why cross game chat is available on the 360 but not ont he PS3.
Honestly, while I have a PS3, it never even crossed my mind that I ought to pick this game up for anything other than my 360, because that's where my friends are at. I try not to rag on the PS3's various network related woes, because for all it's failings at least it's free. I can overlook a lot when it's free.
That said, I do have to wonder - is the OP using a bluetooth headset or not? I always had an issue with choppy audio using ANY bluetooth headset on my PS3 but it works fine using a USB headset I happen to have lying around.