Buying Diablo 3 in a different region
I have seen this post about if I can change regions, but it doesn't seem to answer my question: Can you play with someone in a different region?
Example: I am in the North American Region, can I play with a friend or send an invite to someone in the EU Region? Or do I have to create a character in their region (or vice versa)?
(I would presume you cannot as per the same reasons why you cannot change regions on-the-fly: such as impacting the AH communities by trading between different region characters - etc)