I'm a CT resident with an office in Stamford, CT and an office on Park Ave in NY. At the Park Ave office (32nd floor), my company Verizon Blackberry is lucky to get one bar on the signal strength meter if I hold it to my office window. I literally have to take calls leaning my head against the window. My iPhone 3G and now the i4 are just fine in the office and anywhere on Park Ave from Grand Central up to Central Park. I think a lot of people complaining about AT&T coverage in Manhattan are living or working around Wall Street. By all accounts AT&T has problems in that area.
I use the iPhone every day commuting either the I95 or Merritt Parkway corridors through Fairfield County in southern CT. Coverage is great!
Likewise the metro north train ride into Manhattan has zero dead spots with the exception of the tunnels inside Grand Central. Inside the terminal building is fine.
I've used the iPhone from Boston down to DC along the East Coast with great results.
I've used the iPhone in Chicago without problems.
The two places I found to suck pretty badly were both in CA. San Francisco at the Four Seasons Hotel and at the Ritz Carlton resort in Dana Point just south of Long Beach. It was rather funny. We had about 400 people at a corporate annual meeting with investors. No one had service. Not AT&T users, not Verizon users, and not Sprint users. We came to the conclusion that the resort was jamming cell towers to force us to use their land lines. Watching a herd of crackberry users forced to go cold turkey was hilarious. They refused to give up. Maybe on the balcony. Maybe down on the beach. Maybe at the entrance. Maybe on the restaurant patio. Hey do you have service? No, do you? What carrier? Sprint, what about you? Verizon. I just started lying to friends telling them the iPhone worked great
Also, I don't travel the rural byways of America that often but I'd bet when you're off the interstates in Jackwater Hollow or some such place the signals can be pretty spotty for all carriers.
