If you need to determine the telephone number associated with a phone, you can call your own phonemail number, leave a message and then check your messages and, if the system provides callers' numbers, get the number you called from or you can dial MCI's 1-800-444-3333 number. An automated system will read the number you are calling from to you.
If you need to know the long distance carrier associated with a phone line, you can dial 1-700-555-4141 from the telephone you wish to check. You will hear an announcement telling you the name of the carrier.
And according to the sprint gives out customers data when you call article posted on digg, you can call 1-877-785-8414, which is a Sprint customer service line, put in any Sprint customer's phone number and get the full name and street address of the account holder. The number you are calling from doesn't matter.