Holding naturally, Anandtech measured the iPhone 4 losing 19.8 dB vs the Nexus One 10.7 dB. Keep in mind that dB is logarithmic, so the iPhone 4 performs ~10x worse than the Nexus One in that test.
Signal theory traditionally operates with log scale because it simplifies math greatly and makes graphs manageable. If you say have noise floor at -30dB, expressing it on a linear graph is not very convenient.