I just got a 7100g from Cingular 3 days ago, and for what it's worth, I have considered returning it because of the voice quality. (My Nextel i90 has better voice quality.)
Now, consider the fact that I am currently using two phones and compairing the differences between the two in terms of call audio. Even people I have called have told me that my audio is muffled or that it sounds like I'm talking through plastic.
I spoke to my father on the 7100g right after I got it. He said that it sounded like there was water running in the background. (The air conditioner was on high and when I turned it down, the audio got better and the watery sound reduced.) I frequently use my phone in high noise environments so this may present a problem for me.
Honestly, I'll have to say I'm a little dissapointed in the call quality. I was looking forward to using the Blackberry, and I don't want the larger models.
In my opinion the 7100g feels cheap. I hope I don't ever drop it. The battery door is loose and has some side to side play. The speaker phone audio sounds tinny and has poor quality. Now, these are just my observations and again I am compairing it to a the phone I currently use.
Oh, by the way, for a compact keyboard, I am impressed with the Sure Type. I composed a 50 word email to my brother yesterday and it worked perfectly. My brother also has a 7100t from his company and he said the sure type is great. (This is after using a larger Blackberry for a couple of years and composing hundreds of emails in it.
Hope this helps some.