According to AT&T’s the Samsung BlackJack that was manufactured between November 2006 and February 2007 are faulty, so they have all been recalled.
It has been said that there is an issue with the antenna, there is internal component that is wearing oddly over time and causing the antenna to loosen and disengage, which causes the phone to loose signal and drop calls.
If you are the owner of a Samsung BlackJack then it’s probably about time you got on the old blower and sort it out before it’s too late