We live long distance from family, and told them all by phone last time. At least, I told my family by phone. DH might have sent an email. This year, we'll be there at Christmas and it will all work out.
I just want to point out, though, that telling by phone isn't the end of the world. As long as the important people know before you post in on FB or something, you should be fine.
I'm kind of wondering how your mom will react if (as you said) she tries to make every situation about her. How do you think she will react? That might be a better announcement to make by phone. There were some posts on here over the last few weeks where ladies posted that their moms did not respond with the expected "overjoyed grandma-to-be" reaction.
Or, could you stop by your uncle's house before your mom's house? That way, you might avoid the "Why aren't you staying?" drama. Of course, that might cause "Why did you tell them first?" drama, but it really sounds like your mom will cause drama no matter the situation.
Do what is best for you. Don't set yourself up for a stressful holiday.