Asterisk VoIP to VoIP

Is it possible for one SIP Asterisk user to call another SIP user that is served by another SIP server with URI?

For example, if I setup an AAH at home and you have a AAH at home, can I call you via SIP just by dialing your URI (e.g. sip:john@sip.yourdomain.com)? How to setup SIP Trunk, if needed? Thanks!