These codes work on most HTC Mobile Phones to hidden functions that you can’t change through the phone menu activate & deactivate more advanced.
1. This code for getting Phone information: *#*#7780#*#*
2. This code for getting Battery information: *#*#7780#*#*
3. This code for getting Battery history: *#*#7780#*#*
4. This code for Bluetooth test: *#*#232331#*#*
5. This code for Showing Bluetooth device address: *#*#232337#*#
6. If want to test your LCD press this code: *#*#0*#*#*
7. If want to show your RAM version press this code: *#*#3264#*#*
8. This code for touch screen version: *#*#2663#*#*
9. This code for touch screen test: *#*#2664#*#*
10. This code for proximity sensor test: *#*#0588#*#*
11. This code for Melody test: *#*#0673#*#* OR *#*#0289#*#*
12. This secret code for Showing WiFi MAC address: *#*#232338#*#*
13. By using this secret code you can test your GPS: *#*#1472365#*#*
14. This code for another GPS test: *#*#1575#*#*
15. This code for PDA, Phone, H/W, RFCallDate: *#*#4986*2650468#*#*
16. This code for PDA and Phone: *#*#1234#*#*
17. This code for FTA SW Version: *#*#1111#*#*
18. This code for FTA HW Version: *#*#2222#*#*
19. This code for PDA, Phone, CSC, Build Time, Changelist number: *#*#44336#*#*
20. This code for Packet Loopback: *#*#0283#*#*
21. If you want to test device press(Vibration test and BackLight test also): *#*#0842#*#*
22. If you want know usage statistics press this number on your mobile main screen: *#*#7780#*#*
23. By using this code you can opens a File copy screen where you can backup your media files e.g. Images, Sound, Video and Voice memo: *#*#197328640#*#*
24. WLAN, GPS and Bluetooth Test Codes: *#*#232339#*#* OR *#*#526#*#* OR *#*#528#*#* – WLAN test (Use “Menu” button to start various tests)
25. Please be careful as it’s not always possible to undo the effects of a code (e.g. factory reset): *#*#4636#*#*

Tested/Working:
##775# - EPST/PRL - PRL Settings
##786# - EPST - Status Menu
##3282# - EPST - Data Programming Menu (User Name, Advanced, Restore, Enable HFA, DSA Server, MMSC URL)
##33284# - Debug - Debug Menu – (Debug Screen, Test Calls, RC Data, HDR/1X Selection, Voice Privacy, DTMF Set, Korea Mode Set)
##3424# - Diagnostic - Connect to phone in diag mode
##2539# - EPST/A-Key - Data A key menu
##7738# - EPST/P_Rev - Protocol Revision
##8626337# - EPST/Vocoder - Unsure
##4772579# - Reset the GPS
##72786# - changes DSA back to Factory
##889# - enables TTY
----- Was only able to get the following working on CM6 Rom -----
*#*#4636#*#* - Phone Information - "Phone information, Battery information, Battery history, Useage statistics, Wifi information"

Confirmed not Working:
##UPST# - modem directory
##778# - EPST - Advanced Programming

Unverified:
##37872# - Full Speed USB Mode - Enable/Disable
##3386# - DDTM - Enable/Disable
*#0*# - Test Utility - SAFE TO PLAY WITH
*#0011# Service menu
*#0228# Battery Status
*#0283# Receiver Packet loopback
*#0289# Melody Test again?
*#0673# Melody Test SAFE TO PLAY WITH
*#0782# RTCTimeRead displays time (and seconds)
*#0842# Vibration test SAFE TO PLAY WITH
*#147852# Allows you to access many screens including CDMA DATA Connections
*#1472365# GPS Setup
*#1575# Service menu
*#197328640# Service menu
*#2263# ??
*#232331# Bluetooth RF Test Mode
*#2454# Low Battery Power Off
*#2580# Service menu
*#2663# Touchscreen Accuracy Test SAFE TO PLAY WITH
*#2664# Touchscreen Firmware Version
*#2664# Main Firmware Update
*#2767*2878# Service menu
*#32489# Service menu
*#3264# RAM Version
*#3282*727336*# Current Data State
*#369852# Allows you to access many screens including CDMA DATA Connections
*#4238378# Service menu
*#6984125*# Service menu
*#7284# Service menu
*#745# Sec_RIL_Dump allows you to copy to phone memory, clear ril log, (greyed out copy to SDcard and view RIL log), exit
*#7450# Phone Dump Mode Disable
*#7451# Phone Dump Mode Enable
*#767*3855# Factory Format – CRAP!! WARNING!!!
*#7780# Factory Reset
*#9090# Service menu
*#9900# SysDump copy logcat/dumpstate/dumpsys, enable debug log, copy watchdogdumpstatelog)