[Users] Question about changing an coming call destination.

Hi All, I am having a problem to do the following. A call recevied from PSTN Caller is 1234 Callee is 5678 Normally, the UA 5678 that registered on the openser will receive the call and have caller id display 1234. What i want to do is the UA 1234 will recevice the call instead 5678, i don't care about the callid (basically, caller id will remain 1234). where should i preform the modification? I dont need Callerid. so i just want to send the incoming call to the account that match the caller id. My logic will be if sip_to = 5678, then change sip_to(5678) to sip_from(1234). send the call to the user 1234. However, i am not familiar with the code. Can someone show me how i can do that please? Regards, Howard