[HD2 Android Q&A, Help & Troubleshooting and Genera] BMXJeff:
After an hour or two of frustrating googling and thread sifting I managed to successfully setup A2SD to increase internal phone memory without affecting my current ROM and installed apps/data/settings. I thought I'd put together a clear and simple guide to save anybody else the pain and because I feel I owe the community for all the awesome ROMs and hacks my HD2 has been subjected to over the past couple of years!

Update: If you want to upgrade your ICS ROM rather than fresh install and maintain this A2SD script then see here

How to setup A2SD on the HD2 without flashing a new ROM and maintaining all apps, settings and data

1.) Copy the contents of your SD card to a PC so it can be restored later. Before doing anything like this I always make a backup of my current ROM using CWM recovery and you should too! Please search XDA if you are unsure on how to do this. There are other ways to back up your SD card and apps and tools that will do this for you but this is the easiest and most foolproof method.

2.) Reboot your phone into recovery. If you have MAGLDR then when your phone is off, hold power button until you see the MAGLDR menu and select option 8 for recovery using the volume buttons to scroll and call button to select

3.) Still using the volume and call/back buttons to navigate the menu, select ADVANCED and then PARTITION SD CARD. Select your ext partition size. 1024 seems a healthy size big enough for most people. I have read many warnings about using 2048 and above so I recommend only going as big as you need to. Select 0M swap and continue to partition. Please be aware that your SD card will be formatted so make sure you paid attention to step 1!

4.) Now you need to flash the script that will make this partition wizardry happen. Download 40ad2sdx-a2Recovery.zip and save to your PC. From the CWM recovery main menu, select MOUNTS AND STORAGE then MOUNT USB STORAGE with your phone plugged into the PC. Windows will recognize your phone as a USB mass storage device so you can copy the script (40ad2sdx-a2Recovery.zip) directly onto the SD card. Once copied, press the call button on the phone to unmount USB storage. Now, back to the main menu and select INSTALL ZIP FROM SD CARD then CHOOSE ZIP FROM SD CARD. 40ad2sdx-a2Recovery.zip will be the only thing in the list so select and install it

5.) To complete the setup of the script you need to fix permissions. Once again, CWM recovery does all the hard work for us so from the main menu simply select ADVANCED and then FIX PERMISSIONS

6.) Ok. The A2SD virtual internal phone storage is now setup but before you reboot the phone, you need to restore the contents of the SD card so that Android doesn't try and set up the SD card from scratch and inevitably cause issues with your apps. As in step 4 connect your phone to the PC as a USB mass storage device and copy the SD card backup you made in step 1 back on to your SD card. This may take a while depending on how much data you have. 4GB took just over an hour for me. Once complete select UNMOUNT on the phone

7.) Now for the moment of truth... Keep your fingers crossed and select REBOOT from the recovery main menu. If all went to plan everything should look exactly as it did when you left it. Go into SETTINGS/MANAGE APPS to see your shiny new internal storage size and no more complaints from Android about your internal memory being low.

8.) We're almost there. Although everything should now work perfectly and your internal memory has increased you will most likely find you have the low sound issue where media played from the SD card is very quiet. To solve this you simply need to fix permissions one last time. Boot into recovery as in step 2 and select ADVANCED and then FIX PERMISSIONS just as you did in step 5. Now reboot and enjoy!

WARNING

- This guide assumes you have recovery etc. installed (see my signature for the specs that worked for me)

- I have only tried this with tytung's NexusHD2-ICS-CM9 V1.2 so I cannot promise it will work with other ROMs although I don't see why not. Be aware that some ROMs are already DATA2SD enabled and will not require an additional script - do your research!

- I have written this guide with the intent of helping a few lost HD2 users and it's merely based on my experience. I hold no responsibility for you bricking your phone or any other damage caused

- I am not a DEV but a ROM dabbler; I did not write this script and can only thank the guys responsible for it