Field test mode has announced its return to iOS 4.1, and while this will not mean much to the average iPhone 4 users, those who are more technically inclined will be stoked as this means you will be able to satisfy your curiousity as to how your iPhone 4’s reception is like in real terms (dBm) compared to signal bars. For those running on iOS 4.1, just type *3001#12345#* on your handset and hit dial. A negative number will pop up, and if the absolute value of that number is higher, then that corresponds to a lousier signal strength. To put things in perspective, a measurement of -110 dBm is far less desirable than -85 dBm. Whenever you’re done with the field test mode, just hit the Home button.