Hi there, just to clarify - there is currently no crossover from an EU account to a US one (and vice versa). That is to say that each of the regional games are completely separate and there is no cross-functionality. What you and your friend may want to do is to have one of you send the other a
Recruit-A-Friend link, and then that person could start a new account in that other region. The downside is that the new account would yet need to be upgraded, but the good news is that you'd both enjoy bonuses out of the promotion which would help new characters level 3x faster for 90 days. I hope that helps!