I know we have discussed this in the past, and the search function on the board isn't working right for me now, or I would just find the old post that way.
what is the process for changing the signal strength bars from bars to numbers on the 3g?
Actually a more determined search turned it up. Once you Dial in that code to get into field test mode...hold home down until field test quits. The numbers will now stay. You can tap them to change them back to bars.
It is a number in dBm. Decibels of milliwatts. For hand held walkie talkie type radios, they will work great down to -120, but for the kind of data transfer on a cell phone, we need something a bit better, like -105. Once you're worse than -100 you can basically consider it a 'low' signal. Where it actually stops working will depend on how much noise there is in your area.
It is hard to get a feel for it if you haven't worked with it your whole career like I have, but if you're getting -90 or better, it should be a pretty good signal relative to local noise. If you are dropping calls in better than -90 its a phone or network (or noise) problem, not really a signal level problem.
Cell systems are actually pretty cool and efficient. A standard 802.11 wifi stops working around -80. -80 is a receive power of 0.00000001 thousandths of a watt. So still being able to transfer data from your phone around -105 is pretty darn impressive.