More bars in more places?

For the past year i was part of Verizon and I never had a problem with coverage and signal strength. But now, I swing from 4 to 1 to occasional drop out in my apartment with AT&T. This morning I went to Target and had "no service" while inside. Is this a problem with the iPhone or AT&T?
I know this is the first generation of the phone, but im sure when this thing was in testing, someone must have noticed the weak signal, especially when having a phone company that advertises "fewest dropped calls" and "more bars in more places".
Would all the new iPhones jumping on the cell towers have something to do with it?
imac g5   Mac OS X (10.4.10)  


As I provided with my previous post, I wouldn't get too hung up on the number of bars with 3G access.
There is a restaurant near my house that I frequent. Reception with my first generation iPhone inside this restaurant was always one or two bars. The restaurant has a metal roof which affects reception which significantly improves when stepping outside. EDGE access speed was noticeably slower than normal most of the time when inside.
With my 3G iPhone, it indicates one bar of reception when inside this restaurant but this has no noticeable effect on internet access speed via 3G. When I step outside and 3G reception jumps to 3-4 bars, internet access speed is probably a little bit better, but not noticeable. I can't tell any difference.
I can carry on a conversion with one bar of reception with 3G access with little or no static at times, but not the same with one bar of reception with EDGE. And I can place or receive a call when actively accessing the internet via 3G access - one bar of reception or 5 bars of reception, or anywhere in between which isn't possible when connected via EDGE.