How to Get SIP Header : To Field?


I’m using Asterisk (1.2.4) as a voiemail system for our Softswitch.

When forwarding a call to Voicemail, here is somehow what the softswitch sends to Asterisk :
In INVITE : Vm Phone Number ( to route the call )
In To : Person who has been called !
In From : Person who was calling !

Of course, I need to send the call into the “Called User” Mailbox (Thus To SIP header) !

So Basically, filed in INVITE is “EXTEN”, From field can be obtained from the function ${SIPCHANINFO(from)}
But how to get the “To” field ?

I have tried to add some code line into the chan_sip.c …
It works partially … meaning that, I can add this “to” in SIPCHANINFO funciton,
but the result is null.

Here is what I have added in chan_sip.c :
in structure sip_pvt ( “to” field same as “from” )
in sipchaninfo_function added “to” Line same as "from"
function_sipchaninfo_read added “to” line same as “from”

So I believe that I have enabled somehow Asterisk to read the value to from the channel …
But how to get the value and put it inside the channel ??? I think this would be my real question !

Thanks in advance for anybody who could help me …