According to Global Village Communication (GVC), ALL settings in the Teleport control panel should be OFF (unchecked). Also, the radio buttons for error correction should be set to OFF.
The Apple Internet Dialer sets the modem initialization string to AT&F1&K3. According to Global Village, if you have difficulty using this string, change this to AT&F1 (which GVC's recommended default setting and is the same as a generic modem in the AICK Dialer).
You can change to this string either by selecting 'generic' as the Modem Type or by selecting and editing Add/Modify Modem Type in the Dialer's pop-up dialog box..
Global Village notes that it may also be necessary to append the string with &D2, a command which writes out all the buffered data and then hangs up at the end of the session. In this case, the edited string would be AT&F1&D2.