My iPhone 4 signal does indeed drop from 5 bars to 1 bar if I hold it so the lower left corner is enclosed by my palm. If I switch hands, so I touch the lower right corner, it goes right back to 5 bars. The transition takes about 15 seconds, but I can do it every time.
Remedy #1: scotch tape. Does not help.
Remedy #2: putting leather slip case between hand and phone. Works but awkward.
Remedy #3: a 0.25" x 1.5" piece of gaffers tape on the lower left corner, from the speaker edge up, solves the problem. Ah, gaffers tape, you miracle of technology!
Update: I can't make the problem happen at work. Signal probably is much stronger than at home.
