How to use AT command to detect phone line is busy

Question

I have a USB modem. Is it possible to detect the phone line is busy or not?

I thought I could use AT Command to detect dial tone, but I'm not sure are there any commands support that.

Thanks.

Answer 1

I believe you have to do this the same as a human would... take it off hook and wait for dial tone.

Ripped from http://michaelgellis.tripod.com/modem.html

D alone will take the modem off-hook and wait for a dial tone. (see X command for exceptions). The length of time to wait for a dial tone before dialing is programmable in register S6.

Answer 2

如果您尝试呼叫，但它正忙，调制解调器会向您发送消息BUSY或NO ANSWER