I am using the S46 in the bay area. In general the coverage is very good on
GSM, and where GSM does not work, like in some rooms of my house it works
fine on TDMA.  Also penetrating a large building (> 100,000 sq feet) where I
work is also quite good.  Oh and I live in the bay area.
Regarding usability, the menu structure is arcane and much worse than a
Nokia (which is very straightforward) and a Motorola.  But for basic phone
functions it is fine.

I have a S46 and live in Orlando, FL. The phone works fine. I drove up to my
brother's on the east coast of MD, east of D.C. and the coverage was
continual. HOWEVER, the phone will select a non ATT GSM signal over an ATT
TDMA signal. The phone displayed an unusual carrier name most of the way but
I didn't get charged roaming. The customer service guy can't explain it. I
have the 39.99 ATT National plan. Supposedly if the phone displays ATT as
the carrier I'm on my minutes. If is doesn't I get charged roaming. The
phone did display ROAMING for about 60 miles in S.C. or Georgia.