I have tried Call Forwarding if "Busy" with various cellphones. I noticed that if I press the 'Disconnect' (or 'Hangup') key when there is a incoming voice call, the call is diverted/forwarded to the phone number set for "If Busy" condition.
Now I am trying to implement the above scenario using GSM Phone/Modem and VB.NET.
I am able to set the Call Forwarding phone number successfully using AT+CCFC command. I am also able to detect a incoming call and the caller identification.
However, my problem is that when I receive a incoming call, I am not able to simulate the equivalent of pressing of 'Disconnect/Hangup' key. I have tried sending ATH and AT+CHUP commands on detecting a incoming voice call, however, that simply disconnects the call and does not forward the call to the phone number set for 'Call forwarding/divert' for 'If Busy' condition. I think this is happening because ATH or AT+CHUP commands disconnect the incoming call without sending a 'Busy' response to the calling phone/network.
I have tried this with wide range of GSM Modems (Siemens, Wavecom, Nokia, Falcom etc) and now I am at the end of my wits.
Can anyone help me as to what is the correct AT command (or a *# network command) to simulate the pressing of 'Disconnect/Hangup' key on a phone, so that I can disconnect a incoming call and simulate a 'Busy' condition??