On the second point, however, I kinda agree. People are mentioning some of the +8XX international codes but we should really go hierarchical. A separate higher level code for Earth, for Moon, other planetary bodies; then eventually higher level codes for solar systems, etc.
I really doubt they'll even be doing phone numbers, though.
Even in this solar system only Venus and Mars can you even think about a phone call from earth - and then only for a few days when the orbits align closely. The rest of the time the latency will be too bad. Even when it is possible you will need special training to deal with the latency - it will be more of a monologue not a conversation, with pre-planed handoff times for the other side to state their bit.
The moon will be possible, but most people who try it will find it annoying enough that they will avoid it. If grandma didn't go with you that it will be the only way to talk to the grandkids so it will be done, but if the moon ever becomes self-sustaining expect that there isn't a lot of communication back and forth.
There is a reason satellite never took off for long distance calls - it works but people hated it because the other party didn't respond fast enough. Geosynchronous orbit is only used for calls where there isn't an underseas cable (I don't know if any such satellites are even left in orbit).
(Maybe that's UK only)
The very first or two digits of any phone number on Earth are the country calling codes. We should add extra digits for a planetary calling code.