Point One: This will have nothing to do with EU regulators because Apple does not have a dominant position in the market.
Point Two: Even if Apple did have a dominant position in the market, it still would not fall under the jurisdiction of the EU regulators because Apple makes the hardware and the software; it does not build software for OEM phones. Therefore, the market is not the iPhone; the iPhone is in the same market as Android, WinPhone etc...
All MS has to do is what everyone else does: run the signup outside the Apple store.
It will be interesting to see who blinks first.