You're suggesting an entire country of millions of people change their phone numbers because America decides that it wants to create a new international area code which happens to match the word "moon" in English?
Yes. It's been done before. And considering the available space, eventually the moon could have more people on it than Thailand.
because America
What makes you think that only one country will use phones on the moon?
Perhaps America should change its country code from +1 to say +889, and open up +100 through +199 for others.