As we continue to test the iPhone 4, we're doing our best to track the handset's signal strength, particularly in light of the ongoing issues with the antenna. Though we've also noticed that we occasionally lose bars when we hold the iPhone 4 on its lower left side, the number of bars isn't the most accurate indicator of a cell phone's reception. For more details, we turned to the iPhone's Field Test indicator, but that option doesn't seem to be available on the iPhone 4.
On previous iPhones, you could access a wealth of signal information by dialing *3001#12345#* on the phone keypad. Once there, you'd see the signal strength in decibels in the upper-left corner of the display and the number of nearby cell phone towers at any given moment. It's all great information and handy for gauging reception.
We've asked Apple for an explanation, but we haven't heard back yet. Whatever the reason, a very handy tool has disappeared from the iPhone 4. On the other hand, maybe we just don't know the new code. If you've had luck, please let us know below.