So I only review this post on Modmyi about how a little user reckoning out because covering the phone with your palm causes the network to drop. Quote:

 

The steel partial of the sim label is not centered and is contacting the sim tray. The sim tray is steel and the sim tray is contacting the outdoor receiver band. Once we hold the phone, this could be causing a sim issue.

  

If when we hold the receiver line on the reduce left it changes the state of frequency, energy or what ever, it competence essentially be messing with the sim card.

Take a demeanour at your sim label and see if the steel is only off core sufficient to hold the tray.

  

I only put a tiny square of thwart fasten right where the sim card touches the sim tray and voila, it worked (kind of). The vigilance still drops if I powergrip the phone though only 1 or may be 2 bars, and I dont see any vigilance shift by somewhat covering of the cut on the sides seem. Earlier I would remove all 4 bars when deathgriped and 1-3 whilst only routinely land the phone in my palm.

 

 

 

Original source:

http://modmyi.com/forums/iphone-news/717006-possible-fix-reception-issues.html

http://www.macrumors.com/2010/06/30/one-possible-iphone-4-antenna-fix-with-mixed-results/