Usually you can't tell that a phone call is being diverted unless there is an obvious delay or an auto attendant asking you for something inbetween. I know services such as Vonage can have multiple different lines ring when someone calls your primary Vonage number, perhaps that would be something you should be looking into? Then again I'm no expert on telephony.
I'm not sure what you're trying to do, but it sounds mysterious to me
.
/ 
