I have problem with a gateway gsm of Portech model MV-372. I can make and revice calls but when i call a busy number 3cx don't understand that this number is busy. I have send a request to Portech support and i have recived this response : Thanks your email Please check Mobile\Settings\Lan answer mode. set it to " answered " also.. you need try SIP\Settings\SIP Responses 183 function.too. Best Regards I have check this sets and i correct this on MV-372 but the problem is not fixed. In a previus release of 3cx this problem was present for outbound call that i made with voip provider, but the new version fix this bug (but not for voip gsm gateway). Can anyone help me, or suggest any king of changes on portech or 3cx. I use 3cx ver v5.1.4510.0. Thanks Buono Jury.