It probably had a modem that didn't pay Hayes to license the patent on enforcing a delay in switching from data mode to command mode (+++ did that, and then ATH0 was the AT command to hang up the phone -- normally you'd have to wait a couple seconds, type +++, wait a couple more seconds, and then you'd get an OK and could type AT commands).

http://en.wikipedia.org/wiki/Time_Independent_Escape_Sequenc...