You may experience a situation where an Unknown Caller, is trying to reach you. First, you will see a "Missed Call" notification from your iPhone:
Within 5 seconds of seeing this, you will then receive the Productive portion of this call.
This occurs as a limitation of the current iOS, and we are working hard at resolving this inconvenient issue. Be assured, that when an unknown call comes through, though you may see the "Missed Call" pop down on your phone, it will be promptly followed by the Productive call.
* Be sure to select your desired call settings for UNKNOWN CONTACTS here.