I've actually had these on my iPhone 4 for about two weeks. If you buy the maximum protection shield (not the full body) it comes with these. It is $25 from zagg but if you just do a simple google search you can usually find at least a 20% off discount code. I bought two maximum protections and one zagg skin at the same time, using a 50% off code I got from signing up my junk email account to their weekly free ipad giveaway they have been running lately.
I didn't have a dropped call issue before installing it, I did have some bars drop but never a dropped call from it or any other reason. With them on I don't even have a signal drop if I try. I'm sure if I gave it a really good death grip I might be able to,but in my natural holding position (I'm left handed and hold it exactly how people say it shouldn't be held) it works great. Now if AT&T didn't try and rape my wallet by sending me a $290 bill instead of the groping bill of $120 it should be.
I like invisibleSHIELDS on my devices, used them on all my MBs, MBPs, and iPhones in the past 2 years or so. They are way better looking than most of the cases available for electronics. Sure, up close they might be a little weird looking but if you install it well it is hardly noticeable and lasts a long time. They also have a lifetime warranty so if yours does discolor or peel up you just take it off and send it in for a new one. The material does have a bit of stretch to it, so be careful when applying it or it can look crappy. Worst case scenario you just take it off and request a new one. On my current one I somehow got a tiny hair in the screen area, but it hasn't bothered me enough to take it off yet.
Hope this helps anyone considering getting these for free or paying for them. I think they are overpriced at regular retail, and not a bad deal if you get them with a discount code. If people really want pics I can track down my dslr.