[Serusers] Contact analyze in Location table

Hi all, We're looking for informations regarding an INVITE action we would like to plan for SER server; We're manufacturing a new SIP phone, and in case of DSL-modem router, we're developing a special REGISTER with 2 Contacts for the same SIP phone: A public IP address, and a private IP address. In each case, SER server is placed on external part. Here is a scheme of what is done: @IP1 SIP phone1-----| @IPWan |---[modem-routeur]-----------(......INTERNET.......)-----------------[Exter nal SER server] SIP phone2-----| Location Table : SIP phone-1 <=> {@IP1 ; @IPWan} @IP2 SIP phone-2 <=> {@IP2 ; @IPWan} What we want to do is following: When SIP phone1 is looking for a call-session with SIP phone2, we want SER server to compare WAN contacts in mysql location table, and in case of same Response (=@IPWan), it will redirect INVITE by sending a "302 Moved Temporarly" to SIP-phone1, with a special new contact as SIP-phone2 private IP address (@IP2). Could anyone ever done that before? Any ideas are welcome. Really thanks for your support. Best Regards. Marc