Called while I was on the other line.
Left no msg.
Attempts to return the call were unproductive (non-working number).
I even tried without the 203 (I'm in the 20 3 area, Western CT).
This number came up on my caller ID as INTL GATEWAY. There was no message left. I tried to dial the number back and the recording said it was a non-working number.
*Update* I called AT&T and they said it's usually coming from a telemarketer that has outgoing calls only for their service. So, technically it isn't a non-working number. It works fine in one direction. Unfortunately, there isn't any way to stop them from calling since they never seem to try to sell anything and just hang up. That seems a little silly. I mean what's the point? Nor does there seem to be any way of finding out who they are.