How to make sip extension have STATIS IP:PORT

Hi, I am using Vonage to register SIP trunk, the problem is Vonage phone number “must be set forward to exactly sip address”. It’s mean:

  1. If I have the registered extension like this: sip:102@
  2. Then I need set phone number of Vonage by setting “forward to SIP: sip:102@”
  3. If customer un-register, and register again, the address changed, so I need to config Phone number forward to SIP again.

So I just want to ask can I make the statis ip:port of the extension? Thanks