[asterisk-users] Say who is using the PSTN?

[Grant Emsley]

I use an SPA3000 to connect to the PSTN (SIP/pstn).  Since I only have one line,
if it is in use, and someone else tries to dial out, they get the
all-outgoing-lines-unavailable message played.

I'd like to find a way to instead tell them which extension is using the PSTN
line.  I know that info is available in the manager API, but I have no idea how
to get access to it from either the dialplan or an AGI script.

The relevant portion of my dialplan looks like this:

[macro-dialtopstn]
exten => s,1,Dial(SIP/${ARG1}@pstn,120,WT)
exten => s,2,Goto(s-${DIALSTATUS},1)
exten => s-ANSWER,1,Hangup
exten => s-BUSY,1,Playtones(busy)
exten => s-CANCEL,1,Hangup
exten => s-NOANSWER,1,Play(number-not-answering)
exten => s-NOANSWER,2,Hangup
exten => s-CONGESTION,1,Playback(all-outgoing-lines-unavailable)
exten => s-CONGESTION,2,Hangup
exten => s-CHANUNAVAIL,1,Goto(s-CONGESTION,1)

Has anyone written anything like this, or have any suggestions on the easiest
way to do it?  I've searched and haven't found anything like this so far.

Thanks,
Grant Emsley