The battery will drain much faster when more power is needed to
acquire a signal. You should try driving from Texas to Arkansas. There
the battery of my 3390 will drain within one day, whereas it normally
lasts for slightly longer than a week in stand-by.

your phone "talks" to the cellular towers and adjusts the amount of
transmit power it uses. so if you're down the block from a mini-tower you
might be able to talk for five hours, but if you're five miles away you
might only get 15 minutes.

so called "standby" time will also be affected a bit, but not as much.
Even though you're not constantsly transmitting when the phone is just
sitting there, there's still periodic backs-and-forths between your
handset and the network.

It's also plausable that the power-down commands aren't working correctly
in the second neighborhood. GSM phones and base stations aren't quite 100%
compatable in all features, so secondary stuff like power management might
not be working for your phone over there. Add to this that when you use
your t-mobile phone in California, you're actually using Cingular's
network. Cingular's system might not be familiar with the specific
commands needed to power manage your phone...

(yes, they're supposed to be standardized, but practical reality isn't
quite the same as theory).