Recently, I bought a headphone come with mic. I plug in the cable speaker and mic from headphone to my modem port (speaker & mic) accordingly. After I dialed a phone number, I can hear someone voice. I unable to speak to them. Why ? I got some advise from my friend that I need to turn on "duplex" mode using AT command. How to execute the AT command ? Any advise ? Thanks.

Connect your modem to your PC Com port, open Hyper Terminal, type the name for this connection then select your modem, press OK.

In next dialog, don't dial just cancel, type "ATE1", you can see anything unless you activate this command.

To on the duplex mode, you have to refer from you modem menual for AT command.