I have been attempting to debug a poor reception problem with my iPhone 4 near my house. It has been confirmed that I reside in a dead zone (I am right in the middle of where 2 towers overlap, so I have the weakest signal from both locations) and there's no incentive from my cell provider to fix the problem since the dead zone is very small.
In an attempt to help document the problem, I wanted to capture the exact cell IDs and frequencies used when I experience reception problems. Activating the iPhone's Field Test Mode is easy enough (dial *3001#12345#*), but I quickly realized that something was off with the frequencies listed under by the UMTS/GSM RR Info panes. It was displaying download/upload frequencies of 1037/812 respectively, which is reasonable, but at other times it would show frequencies like 437/37 which made no sense at all.
After a bit of research, it looks like the the label for that data value is wrong; it should be channel and not frequency. Wikipedia has a list of UMTS (3G) frequency bands and the corresponding channel codes as well as the corresponding list for GSM (2G/EDGE). Channels numbers 1037/812 correspond to the 850MHz frequency band which I know Rogers, Telus & Bell all use in their new 3G network deployments. The other popular GSM band in use in Canada is 1900MHz PCS, and sure enough that's what 437/37 corresponds to. Problem solved!