Samsung Blackjacks manufactured between November 2006 and February 2007 are the subject of a quiet recall due to an antenna issue
The issue is degrading signal strength and it definitely looks to be a hardware issue. You can look under the battery to see if your BlackJack falls within the date range. Actually - heck, if your BlackJack is getting bad reception it's probably worth a call no matter when it was manufactured. They ought to know if the problem extends beyond that 4 month span. Plus, you know, you could complain about the delayed Windows Mobile 6 ROM update. Just saying.