I think it related to the card because we used a software to make calls of different people.
When it call via SIP trunk, it can %100 detect the other side answering, not answering, and rejection.
when it call internal extenision, it also can %100 detect the other side answering, not answering, and rejection.
However when it call landline via your OpenVox A400E card, No way to know wither the call is answered or not or reject!! it only can detect the DTMF keypressing only.
1. you need oen the reverse polarity signal to detect otherside answer of hangup.
after you open reverse polarity signal from the provider. edit the /etc/asterisk/chan_dahdi.conf
and command the busydetect and busycount parameter.