They are companies who hire people to solicit money for a myriad of "causes." Highway Patrol, Sheriff, etc.
They get paid a commission to get your money and only a small percentage of the money actually goes to the "cause."

I keep getting this call on my cell phone, when I pick it up there is no one there and then they hang up the phone. This is getting VERY ANNOYING !!!!

This number called. I answered, told them I wasn't available & asked to take a message.  The wonan said it was a courtesy call & they would call back.  They did...6 minutes later , & they hung up when I answered.  I'm fed up with solicitors who use their cell phones to call & who don't id themselves on the screen.

Called my cell phone and left no message.

Just got a call from this number the lady claiming to be with the cancer association wanting to send a pamphlet to my address to provide food and information to cancer patients even if they were in remission she claims she didn't want any money when I refused pamphlet she just said I hope God watches over you and we disconnected the call

They first claimed to be highway police.. Saying i wasnt in any trouble. Then when questioned said they were just representing the highway patroll and soliciting money.They refused to state percentage of money solicited that they kept. Hung up on me.

Caller ID showed Unknown Name.  They didn't leaave a message.  Callback got a recorded message that they were not available.  If they're not doing anything wrong why do they hide their identity.

Hung up when I answered....called back ...got a recording they are unavailable

Same here.  When I answered the caller hung up.

No name on caller ID.  Hung up when I answered.

NO RESPONSE WHEN ANSWERING

Number showed on my Caller ID but name said "Unavailable".  I did not answer.  They didn't leave a message on answering machine.  I'm sure these are the same idiots that call all the time, only using different numbers.

Called, left no msg.