Patrick Juola says:

My understanding is that, legally speaking, "considering [oneself] to be a common carrier" amounts to exactly nil -- that it requires a special act of some governing body to declare you to be a common carrier.

Not quite. If tomorrow you started a new overnight mail service, you would probably be a common carrier if you acted like one, no act of congress needed. The question is not a simple one. My one conversation on this subject with someone from UUNET more or less went "our lawyers say we should act like one and hope the courts decide that we are right." Perry