Cingular Blackberry Unlock
bq. Cingular customers Try the free route first. Call International customer service (Cingular customer service number is 800-335-4685 24hrs) Tell them that you are traveling and need to roam using another SIM on prepaid. They will ask you for your Blackberry's IMEI and then give you the unlock code. Be sure to have free international roaming feature on your account.
There is also a list of services that will unlock for you on the site.