Who called from 2028005567

Called at 9pm PT, I picked up and they said nothing and it hung up.

received a call with CID: EXCHANGESTUDENT
on 9/13/12 at 7:16pm  
I wasn't home when they called and they didn't leave a message.

ALso received a call with the similar CID: EXCHANGE STUDENT    
but the phone number was 612-808-5636    on 8/7  at 7:28pm.  Could they be related?

They called me today at 6:29pm. I called the number back and a message came on saying they are calling about a foreign exchange... and then the message cut off and the line went silent.