List of problems:

No dial tone exists

No response occurs when you type AT commands

AT commands are not visible

Data is displayed as garbled characters after the connection is established

Modem does not answer an incoming call

Modem does not connect to another modem

Modem disconnects while online

AT command initialization string is not working

Connection errors are occurring

You are unable to connect to an online subscription service

You are unable to connect at 56 Kbps