[Asterisk-Users] FXO "Starting simple switch" after hanging up

[Brad Bergman]

I'm having trouble with incoming calls that start to ring again a few 
seconds after the local user hangs up. I get "Starting simple switch" on 
the FXO port, so it's not just a matter of mistakingly initiating a 3-way 
call on hang up or something. Picking up the ringing telephone will get a 
CO dialtone. This happens, say, 50% of the time for incoming calls, never 
for outgoing calls.

Any ideas what I could fiddle with? I have tried 

exten => s,1,Wait,1 

but this doesn't help. Is it possible to distinguish between caller ID
that is sent as "Unknown" and which is just not sent at all? The latter is
the case on all my phantom calls.