taken from somewhere else...

IMEI Number *#06#
For checking the IMEI (International Mobile Equipment Identity).

Security Code 12345
Default security code is 12345. If you forgot your security code, there's so many program on the net which allowed you to know the security code likes Security ID Generator, Nokia IMEI Changer, etc.

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

SIM clock *#746025625# [*#sim0clock#]
to check if the Sim-Clock can be Stopped. This option is depen on your service provider network. (Sim-clock-stop is a kind of standby mode which will save battery time)

Waranty Code *#92702689# [*#war0anty#]
Menu:
1. Displays Serial Number.
2. Displays the Month and Year of Manufacture (0698)
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)
5. The next screen has Transfer User Data? (the same option as the 8110)
6. To exit turn the phone off and then back on.

SP Lock The Service provider (SP) lock
Is used to lock the cell phone to the SP's SIM card. Once the cell phone is locked to a specific operator, if one inserts a SIM card from a different operator the phone will refuse to accept it!
The cell phone will however accept another SIM card from the same operator.

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

The main code used in Nokia

#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.
     
     
eq. 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)

eq. 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!

Unlock SP-Lock
Here is a way to Unlock your phone which is Service Provider locked, without to know SPLock code. With a Nokia 16xx/21xx/31xx/51xx/81xx that are SIMlocked to one privider you can bypass the SP lock like this:

First of all, PIN CODE MUST BE ON, then press:
C
<arrow down>
C and hold until it clears display
* and hold until start to blink
* and hold until start to blink
04*<your pin>*<your pin>*your pin>#

Each time you turn your phone OFF it resets the lock, so this need to be done each time you'll turn your phone ON

The phone now says: PIN CODE CHANGED (or ACCEPTED)and the SIM card is accepted until you restart the phone again.
NOTE: On vesion 5.04 Nokia has removed this option !

Bypass the SP-lock
With a Nokia 16xx/21xx/31xx/51xx/81xx that are SIM locked to one privider you can bypass the SP lock like this:
1.Insert sim card of diferent provider.
2.Turn on the phone and press the UP VOLUME key for 3 sec. then release it and the phone says PIN CODE ?
3.Press the "C" key.
4.Then Press * and wait until it desapear and apear again, then press * one more time and 04*PIN*PIN*PIN#
The phone now says: PIN CODE CHANGED (or ACCEPTED)and the SIM card is accepted until you restart the phone again.
update:On version 5.04 Nokia has removed this option !

Enhanced Full Rate Codec (EFR)
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)

---*3370# and EFR will be activated after a reboot of the phone ( consumes more power )
---#3370# and EFR will be switched off after a reboot of the phone.

Half Rate Codec (HR)
Half Rate will give you bad sound quality, which gives the service provider 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)

---*4720# Half Rate coded will be activated after a reboot of the phone ( better standby time )
---#4720# Half Rate coded will be de-activated after a reboot of the phone

Unblocking Code
---Unblock PIN1 : **05*PUK*newPIN1*newPIN1#@
---UnBlock PIN2 : **052*PUK2*newPIN2*newPIN2#@

Hiding your phone number
Dial 141 then the number you want to call eg. 141#######
This should stop your number been sent to the caller. (*)
(*) This only works on UK phones, if anybody has tried this and works, please let me know.

New Menu on Emergency Calls *3001#12345#
Brings a new menu that gives you access to the emergency calls ( 911 Etc. ). It will give you FREE calls! (only the ones you put in the emergency!! )

This option will depend on your GSM operator

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.