Creating Resume Call Macro? How Phone BLF Key works?

Hello,

A. I am trying to create an Macro to unhold a call.
B. because of A, I am trying to figure out a few things.

  1. When you press on your phone at BLF Key or Speed Dial during a call, what happans behind the scene?
    the phone hold the call(sends a command to the asterisk server) and creating new call?
    or, the phone just creating a new call, and the asterisk server puts call on hold.

  2. I am basically, trying to create a Open-Intercom Macro.
    The macro needs to open the door, so far its easy, i have created the macro bellow as follows, it will call the intercom, send the DTMF to open the door and hangup.

the problem comes, when there is allready an active call while you are pressing the macro.
i would like to extend the macro, so the macro will also resume/unhold the call which the phone have put on hold, prior pressing on the BLF which activates the macro.
A. is that the way to go?
B. If so, how do i do that? I am thinking that phoe signals astrisk to hold the call and play Mousic On hold.
i would like to figure out how can i catch that call ID, so i will know how to resume it, which commands are relative for me creating the macro?

thanks

my current macro at extensions_custom

exten => *00,1,Answer
exten => *00,2,Dial(“SIP/6”,3,M(OpenIntercom))

[macro-OpenIntercom]
exten => s,1,SendDTMF(00*)
exten => s,n,Hangup

Generally with SIP phones you can’t tell them what to do outside of using any proprietary interface they provide to do so. In this case you can’t tell the phone to go off hold, it has to.