I need some help on getting to work my scenario:

I have 3 asterisk servers, and every agents (soft phones like zoiper) is connecting  to which server they need by contacting the PublicIP of each server. (the problem is that I need to reuse the IP address on others servers) .

I want if is possible to use a proxy like "haproxy" but for sip to redirect the agents (softphones), 

to their coresponding server.  

For example: 

- james@ast.example.com -> must register to asterisk server 1, 

- sarah@ast2.exampe.com -> must register to asterisk server 2 

- andy@ast3.example.com-> must register to asterisk server 3

ast.example.com, ast2.example.com, ast3.example.com = will share all the same ip, 

when the request arrives in the proxy it should check the vhost and redirect to the coresponding server for registering.

Any hints and how to do this scenario?