Text or multimedia message to a domestic number cost the same to the domestic sender regardless of the physical location of the recipient. The recipient pays extra to send messages while roaming internationally. Incoming messages to that person are either at the domestic pay per use rate or come out of their allowance, if available.
These are the rules of AT&T Mobility. Other carriers may have different terms. Verizon might bill both incoming and outgoing messages to its domestic subscribers while in Canada at the same rate as messages in the United States.
