My suggestion is...

Cross Server Play


Features:
  • Can friend people from a different server.
  • Can join party with others from a different server.
    When you join a party with someone from a different server you will all have the option to go to each others server or return home.
  • Quest together
  • Raid together
  • Go to the others House

*If it makes it easier just do it for servers only located in your Data Center.
*When someone from another server is on your server it will show their name like such:
NOW:
Icon|Name|<FC>
When your on someone elses server:
Different server Icon|Name|*Server
*Cannot trade with people from different server

...just try to keep it simple.