Telstra rate phone signal sensitivity. The rating is A, B & C.

A: This is the weakest of the lot and in the Telstra phone descriptions it will describe A rated phones as "Recommended for handheld use in metropolitan and major regional areas" – The desire and iPhone4 (amongst others) are "A" rated.
B: This is middle of the road sensitivity and is described as "Recommended for handheld use in regional areas" on the Telstra website – The HTC Wildfire and iPhone3gs (amongst others) are "B" rated
C: This rating is given to phones that are "Blue Tick" rated and offer the best coverage available. The Telstra website will refer to these phones as "Recommended for rural handheld coverage outside regional centres and towns" – The N95-3 & 6120c (amongst others) are "C" rated.