I know it's kinda of sketchy but have you ever wanted to get someone else's number yet didn't want them to have your real number in the exchange? Or have you wanted to sign up for any number of things only to feel unsure about giving out your real phone number?

Introducing, two services:

Numbr.com
Numbr offer free disposable, real phone numbers.

You can get numbers in any area code that you want. You then select when you want the number to expire – an hour, a day, a week or a month. The disposable number is discreetly forwarded to your real number, so you can get a verification call if needed by the company. After said time the phone number becomes invalid so you never have to worry about any more calls.

Brring
If you need a number that is going to last for longer than a month and you want to make money off of your callers then Brring might be for you.

You get paid every time someone calls your Brring number. The caller calls your Brring number and listens to a short (5 second) advertisement. They are then forwarded right to your normal number without ever knowing what your normal number is.

They have ads about travel, cars, electronics, fashion, politics, etc.

Although I haven't used this service, I was just thinking that one could use this number for those free offers you might see at expo's, fairs, etc. that involve a phone number (since they will not know your real number and you'll be getting money from it).