[asterisk-users] Distinctive Ring for SIP?

[Steve]

Hello,

I've done a bit of research, though obviously in the wrong places.  :)  
I'm looking to set up some type of distinctive ring for SIP phones based 
on the context in which the SIP phone is being called from.  If that 
sounds confusing it isn't.

I have two FXOs connected to POTS, so in essence a caller could be 
dialing us at one of two phone numbers.  Each of those FXOs has its own 
context in extensions.conf.  The contexts essentially grab the incoming 
call and ring a bunch of single line SIP phones.  If no one answers then 
the call is sent to voicemail depending on the number that the caller 
dialed.  The problem is that when the SIP phones ring, there's no way 
for us humans to tell which number the caller actually dialed.

My initial thought was to make some type of distinctive ring to the SIP 
phones to indicate which number the caller dialed, much in the same way 
that the telco does it when someone has the distintive ring service.

Another idea would be to set the callerid on the SIP phones to indicate 
which line was dialed.  The drawback there is that we lose the incoming 
callerid from POTS.  Maybe set one of line of the callerid to the 
incoming line and leave the other as the callerid number?  

Does anyone have experience with setting distinctive ring in SIP in such 
a way?

Steve