Usually we flash the radio to improve signal strength. Flashing the radio doesn't mean that you can use it on different carriers. However, the TP2 has a hacked radio by cmonex/olipro that allows us to use GSM ( sim card ) services in the US on US carriers.. like att and tmobile. There is a little more involved that just simply flashing the radio due to the licensing setup that cmonex implemented. Just find the thread and you'll see what is all involved if you choose to do so.
So since you are not looking to use the sim card, you would be looking at improving your signal? I'm not even sure that there are many radios out there for our TP2's yet..Although I haven't look either. The signal seems excellent on my TP2 (sprint) over my tp1. Night and day I would say....that even rhymed.
Hope this clears it up for you.
Oh and welcome to PPCGeeks! Enjoy your stay, there is alot happening in the rom development area since the HSPL just was released. Look for some more great roms and whatever else these geniuses come up with.