Can I purchase a copy of Diablo III from the US Blizzard Store to play on EU server?

Because of the ridiculous price difference Between the US and EU Blizzard Stores ($60 vs, 60€(~$76), ~27% more), I was considering purchasing Diablo 3 on a US Battle.net account and (as a gift) send the authentication key to my EU account, which I primarily use.

• Would this work? If so, would I be able to play with my EU server friends?
• Does Blizzard have any rule against doing this?

Thanks in advance.

Yes. You can play with your friends in Europe from a US account. Just change your server selection settings in options to Europe

Yes you can do what you want to do. At least, it's technically possible and easy to do. I'm not so sure if it violates any agreements that you make during the purchase from Blizzard.

Anyways: Diablo III includes a "global play" function, which simply lets you select the desired server to play on in the options. This means if you plan on purchasing the game using a VPN or something, you can simply create a US account and then still play with that account from Europe, or you can send the game as a gift to someone via email.

Notice, however, that if you create a US account, your home region will be "US", which means that when the addon for Diablo III gets released, you will only be able to play it on the US release, which is usually 8 hours after EU release :)