The first step is to root your phone. Luckily the program Z4root works as a 1-click rooting solution for the LG Optimus T. This application is no longer on the android market, but you can find it with a quick google search, or even better you can get it from the source at the XDA developers forums here.
The XDA developers are going to come up a lot, because they do a lot of the work in making custom ROMs, rooting phones, etc...
Step 1) Download Z4root onto your computer and load it onto your phones microSD card.
Step 2) Download an APK manager/installer from the Android market. This program will allow you to find the APK file that you just downloaded from the web and put onto your SD card, and install it onto your phone.
Step 3) Run Z4root and root your phone (permanent rooting option).
Step 4) Install custom recovery.
Now, once you've rooted you need to install a custom recovery program, found here.
This program allows you to boot your phone into 'recovery mode', which enables you to flash (install) custom ROMs (like version of the operating system), custom kernals (custom settings that enable overclocking), and perform backups of your entire system and all your apps (using titanium backup and NAND backup). Don't worry about these details for now, just follow the link above and walk through the guide. I downloaded a terminal emulator on my phone from the market in order to enter the commands they have listed. When you download the terminal emulator, open it up and then type "su" without the quotation marks. It will then ask you for superuser/root permission, and click YES. Now you will have a # sign and you can go ahead and type all of the commands listed on the website I linked above. Keep in mind that you do NOT type the # symbol for each command line. The # symbol just indicates that you are in the root directory of your SD card. Keep in mind this command (# mv /system/etc/install-recovery.sh /system/etc/install-recovery.sh.bak) did NOT work for me, but as i've read it isn't supposed to. If you read through the questions and comments in the walkthrough thread for installing this ROM, someone asks about this step not working. The developers response is...
"You don't want that file (referring to install-recovery.sh) there as it keeps recovery from "sticking" its not in all roms usually there ater you do an ota update. That command removes it. If its not there move on to next step."
So as you are going through and entering the commands, keep going even if this one gives an error (check the thread in the link and you'll read cases of other people who have had similar problems, and how they fixed them). As long as you're confident that you've typed in the commands as they are given, just keep going through them and hopefully it will work. Remember these are syntax sensitive, so make sure to copy them VERBATIM.
Now keep in mind, I found installing the recovery to be the hardest part of this entire process. Also remember, all of these ZIP files you download (kernals, roms, recovery, etc...) must be copied over as the ZIP file. Do NOT unzip them and copy the contents to your SD card, this will NOT work. Once you have your phone rooted and the custom recovery install, you can quite easily install ANY ROM you want. This means that when people start releasing their custom 2.3 gingerbread ROMs (which usually come out long before the official firmware update is released) you can be the first one on the block to be running it.
Step 5) Download a custom ROM and flash it to your phone using the recovery you just installed. Now BEFORE you do anything, make sure to run a full backup. In the backup/restore section of the recovery, you want to do a full NAND backup.This custom ROM made over at the XDA forums will really make your phone fly. This one is called the Megatron ROM, and I really like it because it's really fast and pre-overclocked to 730 mhz. It has hardware acceleration enabled and a bunch of other fancy features that are NOT enabled with this phone stock. You will find window transitions, animations, and programs running much faster after installing this ROM. There are LOTS of different ROMs available to install, so head over to the XDA developers forum and check out what there is. I'm sticking with Megatron until android 2.3 gingerbread is released, but there are also other great options. There is even an alpha release of 2.3 gingerbread out right now for the Optimus T / One, although it isn't fully functioning and stable yet.
For the kernal you download it, move the zip file onto your SD card, boot into recovery mode, and then flash it from zip. Then when you reboot your phone you will be able to overclock past 730 mhz up to a stable 806 mhz. I've tried going higher, but 806 mhz seems to be the best stable speed to go with. Now in order to do this, you need the program SetCPU from the market. I had to buy this for 2-3 dollars, and it was worth it because I feel like my phone is a little bit more snappy at 806 mhz vs 730 mhz, but it's your choice. SetCPU also gives the option to scale back the CPU's clock speed when it isn't being used (i.e. when it's idle in your pocket), so I have mine set with a max of 806 mhz, and a minimum of 250 mhz.
EDIT - BIG news!!! You can go through that same process for step 6 to install the kernal for OC'ing, but a new kernal has been released that FIXES THE TOUCHSCREEN BUG!!!! So all of that crazy lag and slowdowns in games when you touch the screen (the CPU usages would spike to 100%) has been mostly fixed. This new kernal also allows overclocking the same as the one posted above at the start of step 6, so I would strongly advise to use this one instead!
Step 7) Here is a link to a thread at the XDA developers forum that was made as a central resource for all things LG Optimus T/One (these two phones are identical). You have the option of installing other ROMs and kernals you find, but these are the ones i've personally tried and that have worked well for me. Also, when a 2.3 gingerbread ROM is released, you can download it, load it to your SD card, boot into recovery, then flash the zip file and BOOM, you'll be running 2.3 gingerbread. Remember, before you do anything with new ROMs and kernals, always do a full NAND and nandroid backup from recovery, and do a full backup from Titanium backup.
Step 8) Unlocking. I found this website to work perfectly for both of my LG Optimus T phones, and I got both codes within 12 hours.
An anonymous poster gave the following type in the comments section on unlocking.
"Also I suggest you add this in ur unlock section: this megatron rom is developed based on LP500, which is identical as LP509 but used by t-mobile in U.K. There is a possibility that the unlock code enter screen does not show up even you have the WIND SIM in place after reboot. Inorder to load the unlock code you'll need to type in: 2495#*500# instead 509, while other ROM developed based by other version require change the 500 to 510/507/511 etc. Mode number can be accessed by click "setting->about phone-> model number..
hope this helps.
make sure the unlock code is 16 digits no more no less...
i wasted four tries by entering 17 digits."
Step 9) Some benchmarks for my phone running the Megatron ROM, overclocked to 806 mhz.
Edit - Video is up! Go to the youtube page to view this video in HD!