While we're resurrecting ancient threads of the past....
I found that my Amaze 4G has HDMI via the proprietary (but back-compat) ExtMicro USB port using a 5-pin MHL-HDMI adapter. But it was hit or miss, and I couldn't figure out why (thought it was a defective handset). I swallowed hard and bought HTC's $30 M500 adapter after reading that it was a "12-pin MHL-HDMI" adapter. Wellllll, HDMI worked fine, and I figured it was the extra pins hidden in the back of HTC's port.
Turned out someone on XDA-developers determined that the extra leads (on his HTC Incredible) include COMPOSITE video (e.g. the yellow RCA plug in stereo+video cabling), left & right audio, what appeared to be a "MIC-in" connection, etc. HTC sold an ExtMicro USB adapter with the 3 RCA cables for the old Incredible. Not sure if that would work with my late-2011 phone. Since the Micro-USB out supports HDMI and HDCP on the conventional 5 pins, I wonder if (and why) they are still including the other lines.... :-\
I had a similar experience with content, HTC Watch shows up on an HDMI monitor just fine, but T-Mobile TV (touted as HD, and super value packed you betcha) which costs an additional $13/month, doesn't show up on the external monitor at all.
Why would they think they could charge more than Netflix does for all-you-can-eat streaming, but not let you use an external monitor, even with HDCP support? Silly.... (imho)