Did you jailbreak it too? I'm glad I did, as it gives me ssh access and I can scp files. Also there are some nice apps, like an ssh server (ssh in to the phone) and a vnc server (not very useful but cool anyway).
I'm going to Mexico next month and may have to unlock the phone. I usually buy a local sim card if I'm going to be in a country for more than a few days.
it's running 3.1.2, and the jailbreak for that on the 3gs is this silly "blackra1n" program which requires that you plug it into a computer and run the app every time the phone reboots, or else you're just stuck at the iphone restore boot screen.
if your phone ever loses power or has to be rebooted while you're away, you're stuck without a working phone until you run the program again, so it's completely not worth it for me.