Sorry, right now I don't think we have a good way to validate international phone numbers, we should fix that soon. The email refusing "+" was because of a crappy lib that I was using, and it isn't terribly high on the list of things to fix.
So, I guess the real answer is that it is restrictive because that was what was easiest.. sorry :(
It's worth hesitating before introducing a confirmation-email step. You're certainly going to lose people every time you increase the complexity of the signup process.
So, I guess the real answer is that it is restrictive because that was what was easiest.. sorry :(