Here are 13 easy steps to getting many cell numbers of the rich and famous:
1. Move to Hollywood.
2. Get a job at Universal Studios (perhaps as an assistant gaffer or best boy grip) and be extremely pleasant and courteous to the stars. (You may get a phone number right here!)
3. Earn a living being part of the crew for five or six years, acting in a few independent films on the side to keep your acting skills sharp.
4. Start auditioning for small roles in movies with people you know thanks to your crew experience or independent works.
5. Work your way up the ladder of success, befriending and using countless smaller celebrities. (You will get numbers here)
6. Become famous yourself. (You will get numbers here)
7. While you continue starring in movies and meeting more famous people, hire a voice coach and start a singing career.
8. Conform to musical norms of the day. (You will get numbers here, though mostly the numbers of crazed fans)
9. Get in touch with Justin Bieber's manager and suggest you two do a song together.
10. When you are Justin are in the studio, have a friend call you and pretend that someone in your family has died. This should be no one in your immediate family, perhaps a cousin or great uncle. That way, you will be distraught at the loss of your relative, but not heartbroken to the point where you just want to break down and cry.
11. Inform Justin that you have to return to a random smallish town (maybe Shakopee, Minnesota, or Lynchburg, Tennessee) for the family member's funeral.
12. As you are leaving, mention that you aren't sure when you'll be back. Be sure to have a few tears running down your cheek (that's what the years as an actor were for!) at this point, and getting a bit choked up is a plus. Tell him you'll send him a text when you get back to town, then remember you don't have his number. Unless he's a much more unkind person than he seems, he will give you his number without a second thought.
13. Success! Continue acting and collaborating with musicians until you have all the numbers you could want.
P.S. This list was made in all honesty, except for a few humorous touches. There really isn't any way that you could get famous peoples numbers except for interacting with them. However, since most famous people have bodyguards who keep away non-famous people, you would likely have to become famous yourself or at least extremely important in your own area of expertise.