I had tested calling extensions (Grandstream GXP2000s) a few months ago with a plain jane installation of Asterisk. At that time, if somebody was on Extension B and another person picks up the phone at Extension A and dials Extension B, one of the 3 remaining extension buttons would light up on the phone and allow the person at Extension A to switch to the incoming call.
But now, using Trixbox, if the same thing happens, Extension A simply receives a busy signal (or gets sent immediately to voicemail).
Is this a call waiting issue? Is there a way to enable this by default instead of per line?