GPS function why do they need Data connection? can someone point out?

[ecgz88]

I'm wondering if turn off data connection , will GPS working? do they need to connect to A-GPS Server first?

the reason why I'm asking is I'm in Canada right now, don't want to occur roaming charge when I go to states. =D>

I just come back from States last weekend, check my unbill usage $2 roaming charge in there, I used Garmin XT and never check Weather etc........any suggestion?

tried "home only", won't pick up GPS Signal at all, keep searching GPS Device
tried "flight mode" will work sometimes, then GPS freeze, have to reboot and put phone backing in roaming mode.

can someone point out what setting should I put?