StealthArmor appears to be more of a self-adhesive covering than a case, but it's supposed to keep your iPhone 4 free of scratches just the same. As it comes with side panels that prevent your fingers from coming into direct contact with the device's antennas - which is supposedly what causes the reception issues - it might also prevent your signal from dropping:
It's not a real solution, in my opinion, as I don't think I should have to put my beautiful gadget into any sort of case to prevent my signal from disappearing, but at least it's decent looking and seems to work.
The StealthArmor is priced at $US25 for the clear version or $US45 for one of the fancier patterned versions. [StealthArmor]