My work-issued iPhone dropped 5 calls today in downtown PDX.
Dude, something is wrong.
My wife, daughter, nephew, and I all have iPhone 4. Live in Lloyd district, work and school downtown. I *never* have problems like what you describe and my download speeds with speediest are usually around 3000 except rare times they drop to 1000 at like a blazer+Winterhawks game or something.
I have noticed a problem when riding MAX a across the steel bridge, the tower hand-off or something right at thy spot is problematic.
Get the app "cell phone coverage" from RootMetrics and start running tests - they have a great site where you can see actual real world cell performance on Google maps. (My buddy and I have a ball going to holes in their map and running tests to fill in the gaps).
Seriously though - Downtown PDX is good to us with 4 iPhones...
Now - skiing on mt hood is a different deal... Coverage there is hit-or miss with AT&T...