Marco.org - My iPhone 4 antenna-gap fix →

It’s the tape trick, but with an excellent substitute for the tape: invisibleSHIELD film. It fits right over the gap and covers the entire left side, so when it’s held left-handed (as I always hold mine), there’s no electrical bridging.

I actually was asking around the Twitter sphere about minimal case solutions and this was recommended by more than a few people. If I ever get an iPhone 4, unless any better solutions come along, this is exactly the solution I’m going with.