Hi,
This might help!
{snip from msdn}
The most common cause for failure is a modem that is physically set using
DIP switches or jumpers to the S0=0 condition (auto-answer disabled). In
some cases, the switch setting will override any command issued to set the
modem to answer after 'n' number of rings (ATS0=n). The next most common
cause for failure is PCMCIA modems connected to a telephone network (either
the PSTN or a PBX-type environment) that is not supplying enough ring
voltage to trip the modem's ring-detect circuit. Unfortunately, in this
case, there is nothing that can be done.
Either way, the best way to test this condition is to use a terminal program
such as HyperTerminal to issue the ATS0=2 command to the modem, and dial the
line the modem is connected to. If the modem does not answer the line, the
modem has a hardware-related problem as described above. If it does, you may
want to add the S0 command to the modem's initialization string.