This is another number which calls with an international country code.  They leave no message and I refuse to answer.

They've called me twice.  Same thing, international code +44.  No message.

They have called me twice also.. Thirty Mins apart.. Any ideas?

I just got called twice from this number as well.  I didn't answer it either.

Same here but I answered and they just didn't say anything.  I thought it was a person on the other end though.  Ya know how sometimes the background noise is a little different, like the air itself has sound but with a machine there isn't any?  hmm...  I also received one from 44-207-403-5019, same situation, five days before.
I looked up the country's extension and it was for the United Kingdom.  (All the epsiodes of Carmen Sandiego are coming back to me now, haha.)