Nokia Secret Code (to see the transmit and receive levels in -dbm):

Dial *3001#12345#

Menu up to Field Test. Choose Enable (or Disable), and press OK.
This will put a new menu item called Field Test on the phone.

Note that if you choose "Enable with Lights" the screen will stay lit,
drastically reducing your battery life while you have the field
strength enabled.

Turn the phone off and turn back on. Field Test will then be in the
main menu (will probably be on, if not turn it on by entering this
menu item and dialing 01).

You'll see the db receive level, something like -70 to -90 (-70 is
better than -90) on the screen of the phone all the time.

To turn Field Test off press 00, to turn it back on press 01.

To remove it from the main menu, reverse the above procedure by
entering the "secret code."

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Nextel Secret Code (to see the transmit and receive levels in -dbm):

# * MENU "RIGHT ARROW" (you must perform this sequence quickly).

You'll see an item called Phone Model, and you can hit the RIGHT ARROW
key to see additional items.

Hit RIGHT ARROW six times, and you'll see a screen full of numbers. The
first number is some kind of quality indicator (22.11 is better than
12.11), and the second number is the cell site you're on. Transmit and
receive strength will change as soon as the phone chooses a new cell
site.

The next number is the transmit power, usually at -00db (full power).
If you are very close to a cell site, the number will be bigger, like
-05db, indicating that the phone has reduced the transmit power output.

The next number is the receive signal strength. -80 is better than -99
(which is pretty bad). I don't know what the bottom row of numbers
are for.

IMPORTANT: These screens DO NOT update - you have to go past them, and
then back again to update them.

You can automate the process by pushing TRACE. The phone will go back
to the regular screen, but the field strength information will
alternate with the regular information. Each time the screen
alternates, it will have the current field strength.

To turn this mode off, reverse the above procedure or turn the phone
off for a moment.

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Motorola Startac 7797 (AT&T) Secret Code (to see the transmit and
receive levels in -dbm)

TESTMODE:

NOTE: This is not for the beginner.  You can really mess up your phone
here.

To enter TESTMODE:
[FCN] 0 0 [*] [*] TESTMODE [STO]
(or [FCN] 0 0 [*] [*] 83786633 [STO])

In TESTMODE you can use your phone as normal, but it will display test
data on the screen (signal strength, etc.).  You can navigate through a 
few different screens of test data using [FCN] [#] and [FCN] [*]. You
can always return to the test data display using [CLR] (if something
else comes on the screen).

Once in testmode, you also have access to one more very important
feature, service mode.  If you press AND HOLD the [#] for a few seconds 
you will get a "US" prompt.  Here you can enter various commands. All
of the commands here consist of a number followed by a [#].

Some of the more popular service mode commands are:

01 [#] Restart (you should do this after making programming changes)
19 [#] Show software version
32 [#] Reset phone to factory defaults

-------------------------
PROGRAMMING MODE:
-------------------------

To enter programming mode:
[#] PROGRAM [#] [SND]
(or [#] 7764726 [#] [SND])

You should get a "Which NAM" prompt.  You probably want to enter 1 for
the first NAM.

You should now see "NAM 1 Edit *=yes #=No".  Press [*] unless you
decide you really don't want to be here.

Now you get a Security Code prompt.  Enter your security code, which is
probably 000000.

Now you'll see your ESN.  You can use the volume keys to navigate
through other options.  When you get to the "To Level (whatever)"
options, you can press the "smart button" to get to other menu levels.
Almost every option has text that explains what it is, so you can mess
around with things.

The PPMsg option on level 4 is worth noting: you can change the
power-on message to your name or whatever.  Just type in your new
message using the numeric keypad ([#] moves forward 1 character and [*] 
backspaces) and hit [STO] when you are done.  Then navigate back to the 
"To Level 1" option and press the "smart button".

To exit, navigate to the "Exit" option (level 1) and hit the "smart
button". To save, just hit [*] to save or [#] to cancel.  You can also
abort programming mode at any time using the [END] button.

NOTE: The [CLR] button will always revert values to their previous
state.  [#] aborts at any time.

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SprintPCS Samsung 3500 Phone Secret Codes

***** Debug Menu:
Hit the Menu Button 
Press 9 (Setup) 
Press 0 (this option is NOT listed) 
Enter the Service Code (maybe 040793) 
You get to the Debug Menu.

You have 4 options 
1. Screen Displays information about the PCS network 
2. TestCalls 4 different numbers that test the phone's reception of
   the signal 
3. Errors Displays the last 20 errors that the phone has recorded 
4. EraseError Clears the above list