*#0000# for checking the phones software (SW) - called firmware revision information.

*#746025625# [*#sim0clock#]  to check if the Sim-Clock can be Stopped 
(Sim-clock-stop is a kind of standby mode which will save battery time) This code doesn't work on SW version 4.59.

*#92702689# [*#war0anty#]  Warranty code.
You don't need the warranty-codes any more - you can 
just scroll through the information like in any other menu. It has the the 
same data as 81xx and 31xx phones (with "Edit" button for purchase date, and "User data transfer").

Menu:
1: Displays Serial Number.
2: Displays the Month and Year of Manufacture (0997) 
3: Displays (if there) the date where the phone was purchased (MMYY)
you can here set the Purchasing Date (Warning: You can only do this once - 
so be careful what you write...) 
4: Displays the date of the last repairment - if  found (0000) 
6: Transfers ALL phone numbers, pictures, sounds from one phone to another (eg. if broken) with 6110 u can transfer all data via IRport.(Transfer user data?) 

LASTEST  Version V. 5.22 (xx-xx-99)

Version V. 5.11 (18-02-98)
- An updated GSM operators' list.

Version V. 5.07 (xx-xx-98)
- An updated GSM operators' list.

Version V. 5.32 (21-09-98)
- An updated GSM operators' list. 

Version V. 5.04 (14-09-98)
- An updated GSM operators' list. 
- Removed option for bypassing Simlock by the procedure **04*PIN*PIN*PIN#

Version V. 4.59 (01-06-98)
- An updated GSM operators' list. 
- Bug reported - Wrong dates in short messages (..as in no dates - only ascii crap)
 

Version V. 4.51 (26-03-98)
- An updated GSM operators' list.

This is what the Nokia 5110 displays when software code is typed.

V 04.51 
26-03-98 
NSE-1

First line:
The Software Version (My guess is that this software has been used in 
previously Nokia-phones, what do you say?!). 

Second line:
The date of the SW release.

Third line:
NHE-8 has something to do with the type of phone you are dealing with. 
Is it GSM 900 (standard), GSM 1800 (DCS1800) or GSM 1900 (PCS1900)? 
Nokia 2110, 3110, 8110(i) are all NHE types. 
The only thing that vary is the code after NHE-  ("8"). 
NHE = GSM 900, NHK =GSM 1800 - The number in the end = the model (2110i = 4 etc.)
The 5110 and 6110 is called NSE-1 and NSE-3...this may be because it supports EFR (?)

Software update, how? 
I have been asked a lot about how to update the software in your cell phones. 
The easiest thing to do is to go to the nearest Nokia 
dealer and make him do it for you. Just remember that it is supposed to 
be free (a receipt is requiet) so don't let him tell you anything else!

All Nokia phones (2110 and newer) have four different SIM locks which can be used 
to lock the phone for upto 4 different providers. But most phones with restriction only 
have one lock activated. ( lock 1)

The main code used in Nokia phones is:

#pw+(master code)+Y# 

This code is able to check, activate or remove Sim card restriction (SP-lock).

Use the * key to get the p, + and w chars.

'Y' has to be 1,2,3 or 4 - depending of what lock you what to deal with. 

#pw+1234567890+1# for Provider-Lock status
#pw+1234567890+2# for Network-Lock status
#pw+1234567890+3# for Provider(???)-Lock status
#pw+1234567890+4# for SimCard-Lock status

(master code) is a 10 digit code, based on the phones IMEI number. 

Eg. To remove restriction on lock 1 type following code:

#pw+(master code)+1# 

If you just want to check your phone use 10 random numbers Eg. 1234567890 
as the (master code)

eg. To check if phone if restricted on lock 1 type the following code:

#pw+1234567890+1# 

Please NOTE that these codes could be used with care!
A user told me that it's only possible to type in about 3 different codes on each lock! 
Then something bad will happen ..therefore be careful!

Half Rate Codec: 
On: Enter *4720# and Half Rate coded will be activated after a reboot of the phone ( better standby time )
Off: Enter #4720# and Half Rate coded will be de-activated after a reboot of the phone

Enhanced Full Rate will give you much better sound quality when you enable it. The new Enhanced Full Rate CODEC adopted by GSM uses the ASELP (AlgebraicCode Excitation Linear Prediction) compression technology. This technology allows for much great voice quality in the same number of bits as the older Full Rate CODEC. The older technology was called LPC-RPE (Linear Prediction Coding with Regular Pulse Excitation). Both operate at 13 kilobits.(but you take up more space on the network, so they can charge you more) - Talk-time is reduced with about 5%

Half Rate will give you bad soundquality, which gives the serviceprovider the opportunity to have more calls on the network, and you might get a lower charge from them. - Will give you 30% longer talk-time.

The 54# Tip:
Type 1#, 2#........54# on the keypad (when you're not in the menu) to get the phone number used for 
with this key when speed dialing.

Larger Number Tip (works in 51xx series)
If you hold the key # while you are in the names list, the telephone 
number can be viewed larger. 

Toggle Headset and Auto settings
1) Try Connect the pin-out 1-2 (in front from the right.) to toggle headset settings 
(The phone will think that you ar using a headset - "headset" is displayed in the LCD)
2) Try Connect the pin-out 2-3 (in front from the right.) to toggle auto settings 
(The phone will think that you ar using it in the car - "auto" is displayed in the LCD)

Crazy 5110
Send a SMS full of . (dots) the it'll go crazy when you scroll the received message in your 5110. 
It doesn't do any permanent damage...it only goes crazy if you scroll the SMS.
I'm not sure if it works with all of the software version but it works with 4.59. 
Doesn't work on SW version 4.53 ..

Your number in your display
1.  Goto menu 3-7 Call cost settings.
2.  Turn ON the Call costs' limit 3-7-1.  PIN2 code Required.
3.  Put in the limit with the phone number.
        eg.  my phone # is 019 2184697
     Enter the limit as 2184697
4.  Goto menu 3-7-2 Show costs in.  PIN2 code Required.
5.  Select Currency.
6.  Enter Unit price : 1
7.  Enter Currency name as 019 (per my phone # eg. above)
Now the phone number 019 2184697 will remains on the 4th row of the display.
Secondly, if you press the # key, it prompt which line to be used; Line 1 or 2.

Special thanks to Stealth, CrashOut and hasni for the information.

First See Schematics
 
 

DESCRIPTION

The cable consists of four parts, the RS232 (DB9 Serial) connector, the 3.3volt power supply, the MAX 3232 IC and the phone connector. 

The RS232 end supplies 12v via pins 4 and 7, through 2 (DI, D2) Schottky barrier diodes to a low power (500ma) 5 volt regulator, the 5v output goes through 3 diodes (D3, D4, D5), each of these diodes drops the voltage by 0.6v, so that about 3.3v is delivered to the MAX3232. 

The MAX3232 is a 3volt version of the popular MAX232 TTL to RS232 convertor IC, that is used by a number of manufacturers for their interface cables. The 2V7 Zenner diodes hold the TX and RX date lines to the phone at a safe maximum limit of 2.7volts. Note that the capacitor on pin 6 of the IC has it's +ve lead to ground. 

The hardest part to get hold of might be the phone connector, you might have to utilise a hands free connector.. 

NOTES

In practice the diodes D1 and D2 can be general purpose 1N4148 diodes, and D3, D4 and D5 can be 1N4001 diodes. The circuit should be built as shown. Be sure to check all solder joints and the orientation of components. 

The above information should be more than enough for the electronic hobbyist to construct a working cable. If you find that it does not make much sense to you DO NOT ATTEMPT TO BUILD THE CABLE, it might save the life of your phone! As I say there should be more than enough information, DO NOT ask me for more! 

Source: www.mobil.cz/telefon/triky/6110/zapojeni.html

1 Laungh the NetMonitor in your Nokia 51xx / 61xx 
2 Execute the test number 497 
3 Free calling for about 90 sec should now have been activated.

The trick has not been comfirmed working yet.

V V 1 2 3 4 5 6 V 
(o) | | [= = = = = =] | |
7 8 9 10 11 12 

1 - VIN CHARGER INPUT VOLTAGE 8.4V 0.8A
2 - CHRG CTRL CHARGER CONTROL PWM 32Khz 
3 - XMIC MIC INPUT 60mV - 1V 
4 - SGND SIGNAL GROUND 
5 - XEAR EAR OUTPUT 80mV - 1V 
6 - MBUS 9600 B/S 
7 - FBUS_RX 9.6 - 230.4 KB/S 
8 - FBUS_TX 9.6 - 230.4 KB/S 
9 - L_GND CHARGER / LOGIC GND