[P3300, MDA Compact III ROM Development] randythered:
Since there are many newbies here who are new to the world of flashing I've decided to do them all a huge favor by posting this thread. If there are other tutorials around, I'd suggest the mods sticky them please. I'm going to make this one as user friendly and easy as possible.

Okay. So you're bored of the stock HTC ROM eh? Never fear, the XDA cooks are here :D

If you are using an XP machine, you are good to go. If you are using Windows Vista or Windows 7, then go to this page and follow the instructions here to roll back the drivers. THIS IS IMPORTANT IF YOU'RE ON VISTA OR 7 BECAUSE OTHERWISE YOUR PHONE WON'T CONNECT IN BOOTLOADER!

Also, take note that while doing ANY kind of flashing, always remove both your SD card and your SIM card. ALWAYS.

Firstly, you will have to CID unlock your phone. Download the USPL and follow the instructions to flash it onto your phone. What, still need instructions? Okay.

Unzip it.

Connect your phone (WHILE IT IS RUNNING, NOT IN BOOTLOADER)

Click start_uspl.exe

Wait till the process finishes.

The phone will automatically reboot. During boot up, you will see a few numbers on your white HTC screen. Look out for the SPL number. If it is 1.11.0000, then you have been successful in unlocking your phone. If not, well, you have to try again. Mostly it should happen in the first go.

Now. Once your phone is CID unlocked, you can download any ROM you want and flash it to your device. Lets say you are kind to me and download one of my ROMs (see my sig :D)

*Before you flash any ROM though I strongly suggest you update your USPL to the new cmon USPL. This improvement lets you flash ROMs of ANY size to your device. To flash this, just download the file, and replace the ruu_signed.nbh file located in any of my (or anyone else's) ROM package with the one included in cmon USPL.

Then, put your phone into bootloader mode. To do this, switch your phone off. Then press the voice recording, power and reset buttons together. After 5 seconds release the reset button, but keep the other two pressed till you see a three colored screen. Once you see the screen you are in bootloader mode.

Once in bootloader, connect the phone to the PC. Once it is connected run the RUU.exe located in the folder where you just put the cmon USPL .nbh file. Keep pressing next and finally press update. It will be done in 2 seconds. On next boot your SPL version will now say 1.11.cmon. Yay, success.

Now you are ready to flash any ROM of your choice. Download whichever ROM you want, and unzip the package into a folder. The package will have around 6 files. Of them, only RUU.exe and ruu_signed.nbh are important. Once you check for these files, put your phone in bootloader mode again, connect to PC and start RUU.exe. Like cmon USPL, keep pressing next and then update. Soon, you will have a progress bar on your phone as well as your computer screen. The flashing process will be complete in 10 minutes.

The phone will reboot once the flashing is done. Now you can kiss old stock ROM goodbye! On system reboot, the phone will take some time to start, and it will ask you to "tap screen to begin setup". Do as the phone tells you to, align the screen, enter the date and time and your new flashed ROM is ready to use!

I hope this post helps all the newbies out there in flashing their devices. Be warned, you have to be careful while doing this or your device might end up as a very attractive brick. It is very easy and I'm sure all you people can manage it.

Special thanks to:

pof and cmonex for their USPLs

All the brilliant cooks of Artemis XDA

*If I made any mistake in this the experienced people can bring it to my notice and I will make changes. Everything is correct best to my knowledge :)