2nd call on my cell phone. May 2nd and today, May 11th. No idea who or what.

Received two calls this week and they just hang up when we answer.  What is the purpose of these calls?

2nd call from this number on my cell. Call terminates when I answer. Sept 2011

I get these calls from many differnt numbers but don't answer them (based on the area code they are calling from).  I get as many as 10-15 per week but don't know who they are from because I don't answer them.  I believe these are automated calls to detemine if your number is available for a call from a telemarketer.  That is why it hangs up when you answer it.  If you do answer it, then an acutal person starts calling.

It is a company trying to get you to advertise in their state manufacturers guide.