The email vendor doesn't really matter though unless you are sending or receiving emails. Phone numbers require you to pay a carrier every month. And while most people have phone numbers, some don't, especially children.
My mum used iMessage to communicate with my sister before she got a phone number. If she switched to Android, I guess there's Google Chat, but you know how Google is with their chat apps.
Ideally you'd be able to choose between phone number OR email. Like iMessage.