Ask him for it.
If you’re interested in a guy, you should feel comfortable enough to talk to him and ask him for his phone number. If he is showing signs of being interested in you, such as going out of his way to spend time with you, showing up in places where he knows you’ll be or telling friends that he likes you, he probably will be more than happy to give you his phone number.
Give him your phone number.
If you’re too shy to ask him for his phone number, give him your number, and when he calls you, his number will show up on your caller ID. Just ask if the number that showed up on your caller ID is his number to make sure he’s not calling from someone else’s phone.
Look online for it.
There are people search sites where you can enter a person’s name and get information such as their address and telephone number. If he doesn’t have his own place and still lives with his parents, then you’ll have to search by the parents' name, because there’s a good chance the telephone number will be in their name (see Resources below).
Request him as a friend on a social networking site such as Myspace or Facebook.
Some people actually put their phone numbers on their personal webpages. If his number isn’t listed on his profile page, send him a message through the site and ask him if it would be OK for you to call him.
Ask someone he knows for his phone number.
If you have a mutual friend, see if this friend will get the guy’s phone number for you. If he has any relatives that you know or are friends with, see if one of them will give you his phone number. It will help if you’re actually friends with the relative so it doesn’t seem like you’re just using them to get his phone number.