Activate an AT&T iPhone 3GS outside of USA after iOS upgrade
Yes - you just need any new or secondhand AT&T SIM to get the device activated. If you can keep that SIM to do the activation so much the better, so having a friend bring one would be easy if you can wait.
The process won't care where in the world you are, just that when the device connects to Apple's activation servers, the SIM number from the card is in an AT&T range. At that point, you'll need to do the jailbreak work appropriate for the device and the OS level but it will work as a WiFi based device with just the correct SIM and no AT&T contract required.