I'm posting this step-by-step guide to help all those who, like me, have problems with receiving/installing the much awaited 2.1 update for their T-Mobile Hero (G2 Touch). It took me a while after figuring everything out by myself since both T-Mobile and HTC support have been absolutely inept at providing a solution.
You may have tried moving the phone's date forward a couple of weeks as suggested by T-Mobile and you'll probably get the pop-up notification window, but when you try and install the update the screen goes black with a warning triangle and it freezes.
1- First of all BACK UP all your data! This is because updating the phone will erase all data on your phone and reset it to it's factory state. I use My Back Up Pro, it's very easy to use and you'll be able to restore everything, from your pictures, music files, apps, etc to your messages, contacts and so on. It will even restore all your shortcuts and replace them exactly where you've placed them on your home screen(s). If you have a lot of files I suggest you back them up online as your SD card may not have enough space.
2- Download and install the latest ROM from the HTC website, you can do so here: http://www.htc.com/uk/SupportDownload.aspx?p_id=283&cat=2&dl_id=775.
This is where some of the confusion arises. You may think that you have the latest ROM on your phone (you can check by going to Settings-About phone-Software-Build number. It should be 126.96.36.199. However if you've downloaded it from the T-Mobile support website it is NOT the same as the one on the HTC website DESPITE having the same number, and it's this that's preventing your phone from receiving the notification for the new 2.1 update and installing it. Confusing eh? So, download the ROM update and install it on your phone following the simple instructions.
3- Once your phone has installed the ROM it will restart. Finally, the notification pop-up will appear! Tap 'Install'. The phone will start installing the update without any glitches. You may also get a second pop-up notifying of a second update. Proceed as before. I suggest you do all this over Wi-Fi as it's a huge file.
4- Again, once the installation is complete your phone will restart and you'll be able to enjoy the new features. It's like having a new phone, better interface, better graphics, better performance!
5- Finally re-download My Back Up Pro from the Market and restore all your stuff. Again, this is best done using Wi-Fi. Notice: When restoring data, if your Contacts and Calendar are synched with your GMail account, UNCHECK these from the list that shows up.
I really hope this goes some way to help all those people who like me have been frustrated with being able to install the update and by the total lack of support from T-Mobile and HTC. Feel free to ask me any questions if you have any, and good luck!