[Asterisk-Users] Detect hangup on unanswered POTS call

[Nathan Lutchansky]

I've been using * at home for a while now and I'm quite happy with how it
works.  Having voicemail emailed to me and notify my cell phone via SMS is
a great way to impress my friends.  :-)  The inbound context for my X101P
looks something like this:

exten => s,1,Dial(SIP/analog1&SIP/analog2,20)
exten => s,2,Answer
exten => s,3,Voicemail(u1234)
exten => s,4,Hangup

The trouble is, some unknown caller (probably a telemarketer, but I have
no CID) keeps calling and hanging up after precisely four rings, causing *
to pick up the line and get a dialtone.  It will happily play the outbound
message, then record 90 seconds of dialtone and hang-up-the-damn-phone
noise.

What are my options for fixing this?

- Ideally, Asterisk would detect the dialtone and immediately hang up the
phone.  Does the call progress detect code do this?  I have busydetect
turned off.

- Incoming calls could be picked up immediately, then receive ringback or
hold music while Asterisk rings the handsets.  Asterisk could then detect
caller hangup with the usual kewlstart signalling.  The problem is that
the caller always gets billed for unanswered calls.  (Although this might 
have the advantage of encouraging people to leave a message once they 
realize they're going to get billed for the call either way.)

- I could add an extra prompt after the outbound message saying "Please
press 1 if you would like to leave a message."  This is extra,
unanticipated work for the caller, and doesn't solve my problem entirely 
because the line is still off-hook until the context times out.  But at 
the moment it looks like the most viable option.

What do other people do to work around this problem?  -Nathan

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