[Serusers] Need to work on subst().

Hi Ricardo , I too need the same process which you had done by subst(); function. two weeks back i had posted a mail to ser-users . regarding this issue. because one call-shop with the small sip-proxy using private ip-adress controls the remaing phones . and with one username i am giving access to all phones so that i can bill for one account only . but when a sip-phone registered to that callshop make call it forwards to my SER with contact id as eg: 12345(a)192.168.2.101 .so, the call comes in as it just requires authorise but when we hung the phone the "BYE" messages are not recieving by both end parties because SER is sending "BYE" messages to that contact-id that is private ip so call became "idle" for 30-40 seconds and after it shut down. so now i need to rewrite the contact part of that private ip-address and just use NAT ipadress of that sip-proxy(call-shop) i saw your subst(); funct. in your mail but i dont know where and how to use that,(I am not a programmer) So how you suggest me to do that for rewriting any private ip-adresss and replacing NAT-address so that the call will ends when it recieve "BYE" message . below is the trace of that: U 82.102.69.105:39871 -> 81.21.33.35:5060 INVITE sip:99106883@81.21.33.35:5060 SIP/2.0. To: "99106883"<sip:99106883@81.21.33.35 :5060>. From: "12345"<sip:12345@81.21.33.35:5060>;tag=c86b66ad8b9187c8. Via: SIP/2.0/UDP 192.168.1.100:5060;branch=z9hG4bK-d87543-bcf89635ebeba2e78782465686dfaf52-1--d87543-;rport. Via: SIP/2.0/UDP 192.168.1.102 ;branch=z9hG4bKf638e18b56022ea3. Call-ID: a78d5c993a9dd6b4(a)192.168.1.102. CSeq: 47344 INVITE. Record-Route: <sip:192.168.1.100:5060>. Contact: <sip: 192.168.1.100:5060>. Max-Forwards: 69. Allow: INVITE, ACK, CANCEL, BYE, NOTIFY, REFER, OPTIONS, INFO, SUBSCRIBE. Content-Type: application/sdp. Supported: replaces. User-Agent: Grandstream BT110 1.0.8.23 . Content-Length: 361. Ricardo here i need to replace contact<sip:192.168.1.100> with above NAT ip address that is with 82.102.69.105:39871 how ??/ please assist me so that i can solve my problem. Thank You. Regards, Ravi.