Every phone loses signal when held by a human hand...the density and magnetic field of a person have to do with this I would think...but the iPhone4 would completely lose signal, I mean from full strength to minimal feedback...my HD7 only suffers from signal loss in my office, which I'm pretty sure is made of adamantium because nothing gets signal in there...everywhere else is just fine...
AT&T Nokia Lumia 900
T-Mobile USA HD7
Windows Phone 7.5 (Mango)
: HD7, HD2, Touch Pro 2, Touch Pro, Dash, and toss in a few Sidekicks for good luck