I honestly think the 3G issues is exacerbated here in the U.S. on T-mobile's network where they don't have "deep" coverage. In larger cities, such as Chicago (where I've tested my theory), no amount of covering the lower back portion of the phone caused me to drop off 3G. I went from 4 bars to 3, and that's about it. Here in Toledo, Ohio, T-mobile hasn't saturated the area with 3G, and covering the phone while indoors drops me to Edge. Outdoors I'm still fine.
Google Nexus 4
Google Nexus 7