From some hotels (e.g., while travelling overseas) telephone
switchboards generates a tone that sounds like an engaged signal until
a 0 is pressed. With this one can not dial up as the ppp chat script
always finds "NO DIAL TONE" and fails. A fix might be:
Replace ATZ with ATH1. May need to extend the time waiting from the
100 (1 sec) standard setting to 250, so the modem doesn't send the
ATDT(phone no.) too soon.