I think what lisamyers was meaning was password codes similar to those on the earlier connection releases that allowed you to get special items (V1-V5.5).
Unfortunately there are no such codes for the Tama-Go (or Music Star) as codes for items and such were individually obtained from the TamaTown website due to your login code, which is no longer active due to Bandai America giving the rights to the Tamagotchi brand to Sync Beatz and closing down the TamaTown servers in February 2013. Sorry about that. :/
This means that even if you were after the login codes for TamaTown that OldSchoolTama referred to above, they wouldn't be of much use now, as the TamaTown servers are closed.