Old thread but someone might find it on a search.
The username and password could refer to either your paired bluetooth connection or to your carrier's conection settings. If it's for pairing, it's whatever you set it up as originally. If it's your carrier's connection settings, the username is generally something like
and the password is the ESN of the handset.
However, I believe that Object Exchange (OBEx) is disabled on most Blackberrys released and will not work as a modem connection. I know it definitely will not work with any Telus Mobility handset released prior to the Blackberry 8703e or Microsoft Q. I tried them for hours when I worked there.