Call came in while driving.  Did not speak and phone hung up.  Probably robocall.

They call and hang up if I try to answer.

2014 - September.
I have received a dozen calls to my mobile phone from number 631.801.7006.
No one answers. I have answered "Hello", "Hello this is Michael", and remained silent. All with the same results.  
When you receive the call, the transmitting end immediately hangs up. The area code 631 is in New York State, in Long Island, in the towns of Babylon, Brentwood, & Brookhaven. As for the Call Type and or nature of the call, I am unsure. I suspect it could be a robot call just to see if the number being called is a valid number. When you pick up the call, the robot then knows your number is a valid phone number in use. Companies sell that information to telemarketers. In my iPhone, I have gone into the recent call list and clicked the "i" for the information. Inside here, I have set this number as "Block this Caller"

calls but doesnt say anything

I get calls from this number and also 7005 7004 and 7003, all are the same company, AVS Solutions, usually a foreign man will say may I speak to the manager, I say I am and they hang up, it is the same thing each time. If you call back all you get is a recording that says press 9 to be placed on the do not call list, This does not place you on a do not call list it simply gives them verification that it is a live working phone number. I believe they compile lists for sale, as often they will also say have I reached US Credit? Again  as soon as I answer yes can I help you, they hang up there is no other explanation for these actions as certainly they cannot be selling anything if all they do is hang up after verifying a live voice. DO NOT call them back and hit 9 or you will never get off whatever list they are selling, I have blocked all of their numbers 1-631-801-7003-7004-7005-7006 again DO NOT call them back and hit 9!!!