[Galaxy S II General] cmpnetman:
Well... I know there are some other posts pertaining to the same subject but I believe this is an exhaustive list.

Galaxy S i9100 Secret Codes

*#06# = IMEI Number.

*#1234# = Firmware Version.

*#2222# = H/W Version.

*#8999*8376263# = All Versions Together.

*#8999*8378# = Test Menu.

*#4777*8665# = GPSR Tool.

*#8999*523# = LCD Brightness.

*#8999*377# = Error Menu.

*#8999*327# = EEP Menu.

*#8999*667# = Debug Mode.

*#92782# = PhoneModel. (Wap)

#*5737425# = JAVA Mode.

*#2255# = Call List.

*#232337# = Bluetooth MAC Adress.

*#5282837# = Java Version.

#*4773# = Incremental Redundancy.

#*7752# = 8 PSK uplink capability bit.

#*7785# = Reset wakeup & RTK timer cariables/variables.

#*7200# = Tone Generator Mute.

#*3888# = BLUETOOTH Test mode.

#*7828# = Task screen.

#*#8377466# = S/W Version & H/W Version.

#*2562# = Restarts Phone.

#*2565# = No Blocking? General Defense.

#*3353# = General Defense, Code Erased.

#*3837# = Phone Hangs on White screen.

#*3849# = Restarts Phone.

#*3851# = Restarts Phone.

#*3876# = Restarts Phone.

#*7222# = Operation Typ: (Class C GSM)

#*7224# = !!! ERROR !!!

#*7252# = Operation Typ: (Class B GPRS)

#*7271# = CMD: (Not Available)

#*7274# = CMD: (Not Available)

#*7337# = Restarts Phone. (Resets Wap Settings)

#*2787# = CRTP ON/OFF.

#*2886# = AutoAnswer ON/OFF.

#*3737# = L1 AFC.

#*5133# = L1 HO Data.

#*7288# = GPRS Detached/Attached.

#*7287# = GPRS Attached.

#*7666# = White Screen.

#*7693# = Sleep Deactivate/Activate.

#*7284# = L1 HO Data.

#*2256# = Calibration info? (For CMD set DEBUGAUTONOMY in cihard.opt)

#*2286# = Databattery.

#*2527# = GPRS switching set to (Class 4, 8, 9, 10)

#*2679# = Copycat feature Activa/Deactivate.

#*3940# = External looptest 9600 bps.

#*4263# = Handsfree mode Activate/Deactivate.

#*4700# = Please use function 2637.

#*7352# = BVMC Reg value (LOW_SWTOFF, NOMINAL_SWTOFF)

#*2558# = Time ON.

#*3370# = Same as 4700.

#*3941# = External looptest 115200 bps

#*5176# = L1 Sleep.

#*7462# = SIM Phase.

#*7983# = Voltage/Freq.

#*7986# = Voltage.

#*8466# = Old Time.

#*2255# = Call Failed.

#*5187# = L1C2G trace Activate/Deactivate.

#*5376# = DELETE ALL SMS!!!!.

#*6837# = Official Software Version: (0003000016000702)

#*7524# = KCGPRS: (FF FF FF FF FF FF FF FF 07)

#*7562# = LOCI GPRS: (FF FF FF FF FF FF FF FF FF FF FF FE FF 01)

#*2337# = Permanent Registration Beep.

#*2474# = Charging Duration.

#*2834# = Audio Path. (Handsfree)

#*3270# = DCS Support Activate/Deactivate.

#*3282# = Data Activate/Deactivate.

#*3476# = EGSM Activate/Deactivate.

#*3676# = FORMAT FLASH VOLUME!!!

#*4760# = GSM Activate/Deactivate.

#*4864# = White Screen.

#*5171# = L1P1.

#*5172# = L1P2.

#*5173# = L1P3.

#*7326# = Accessory.

#*7683# = Sleep variable.

#*8465# = Time in L1.

#*2252# = Current CAL.

#*2836# = AVDDSS Management Activate/Deactivate.

#*3877# = Dump of SPY trace.

#*7728# = RSAV.

#*2677# = Same as 4700.

#*3728# = Time 2 Decod.

#*3725# = B4 last off.

#*7372# = Resetting the time to DPB variables.

#*7732# = Packet flow context bit Activate/Deactivate.

#*6833# = New uplink establishment Activate/Deactivate.

#*3273# = EGPRS multislot. (Class 4, 8, 9, 10)

#*7722# = RLC bitmap compression Activate/Deactivate.

#*2351# = Blinks 1347E201 in RED.

#*4472# = Hysteresis of serving cell: 3 dB

#*2775# = Switch to 2 inner speaker.

#*9270# = Force WBS.

#*7878# = FirstStartup. (0=NO, 1=YES)

#*3757# = DSL UART speed set to. (LOW, HIGH)

#*8726# = Switches USBACM to Normal.

#*8724# = Switches USBACM to Generator mode.

#*8727# = Switches USBACM to Slink mode.

#*8725# = Switches USBACM to Loop-back mode.

#*3838# = Blinks 3D030300 in RED.

#*2077# = GPRS Switch.

#*2027# = GPRS Switch.

#*0227# = GPRS Switch.

#*0277# = GPRS Switch.

#*8370# = Tfs4.0 Test 0.

#*8371# = Tfs4.0 Test 1.

#*8372# = Tfs4.0 Test 2.

#*8373# = Tfs4.0 Test 3.

#*8374# = Tfs4.0 Test 4.

#*8375# = Tfs4.0 Test 5.

#*8376# = Tfs4.0 Test 6.

#*8377# = Tfs4.0 Test 7.

#*8378# = Tfs4.0 Test 8.

#*8379# = Tfs4.0 Test 9.

#*7878# = FirstStartup. (0=NO, 1=YES)

#*3838# = Blinks 3D030300 in RED.

#*2077# = GPRS Switch.

#*2027# = GPRS Switch.

#*0227# = GPRS Switch.

#*0277# = GPRS Switch.

#*22671# = AMR REC START.

#*22672# = Stop AMR REC. (File name: /a/multimedia/sounds/voice list/ENGMODE.amr)

#*22673# = Pause REC.

#*22674# = Resume REC.

#*22675# = AMR Playback.

#*22676# = AMR Stop Play.

#*22677# = Pause Play.

#*22678# = Resume Play.

#*77261# = PCM Rec Req.

#*77262# = Stop PCM Rec.

#*77263# = PCM Playback.

#*77264# = PCM Stop Play.

#*22679# = AMR Get Time.

*#8999*364# = Watchdog ON/OFF.

*#8999*427# = WATCHDOG signal route setup.

*2767*226372# = Camera Reset. (deletes photos)

*2767*3855# = E2P Full Reset.

*2767*2878# = E2P Custom Reset.

*2767*927# = E2P Wap Reset.

*2767*226372# = E2P Camera Reset.

*2767*688# = Reset Mobile TV.

#7263867# = RAM Dump. (On or Off)

*#0*# = testing sensors and other stuff (thanks karfeef)

*#0011# = ServiceMode/Debug/Basic Information (thanks Croak)

Samsung mobile sound code.

Samsung phones.

Dial *#6984125*#

Test menu dial *#9072641*# (You need this one i think.)

Click 5 Audio – 2 AP volume config

Tune Headset volume:

*#9072641*# – 2 EAR config – 3 Ringtone volume – Stap 6 tune it to 10

Tune movie volume:

*#9072641*# – 3 SPK config – 3 Ringtone volume – Stap 6 tune it to 10

Note it works but don’t forget to type somewhere your old settings.

Credit:

Samfirmware