Late reply, but I'm new to the forum. I have had a 3DO case for my HTC Amaze since I got it when it first came out late in 2011. The case is amazing for impact resistance. I have dropped my phone onto concrete many many times and it doesn't have a single scratch on it nor has the screen ever cracked. Watch the Tech21 demo video on youtube, the guy throws his 3DO wrapped phone at the wall several times then drops it off a balcony twice and the phone was fine.
Now, with that said, several times over the course of my ownership of this phone, I have had severe antenna strength issues and dropped calls, and when I've taken it into T-Mobile, after they had done their tests, and no issues were found, they said that there have been other similar complaints, and the other customers with the same problems also owned the 3DO case. I'm not sure if this is really the issue or not, because my phone seems to work fine most of the time when in the case.
All in all, I highly recommend the 3DO cases.