Jason Langridge had an interesting titled post on his weblog this morning Why does your mobile phone never work as well in the US?

Well in the US the GSM Network is made up of 850MHz and 1900 MHz bands. Between the 850 and 1900, the US gets covered completely. In the rest of the world we use predominately the 900MHz band  although many service providers also use 1800MHz.

 

So why do you get such bad coverage in certain areas? Well some places are great for 850 but horrible for 1900 and on the flipside some places have excellent 1900 and are just bad for 850.

 

To make matters even more confusing T-Mobile just got the 1700 band from the government so this will make things even more confusing in the next 2 to 3 years.

The best plan to avoid any problems is to carry a Quad Band Phone - a phone that supports 850,900, 1800 and 1900 MHz : The HTC Touch Cruise, TyTn II, Blackjack 1 and 2 are all Quad Band phones.....

 

The other variation of phone is a tri-band phone (surprisingly a phone that supports 3 bands) - there are normally two combinations of tri-band phones:

900/1800/1900 - Excellent internationally and very good in the US

850/1800/1900 - Excellent in the US but not very good internationally

You can get more details HERE

Source: Jason Langridge