There has been a lot of speculation recently about T-Mobile's Project Emerald. Some of the more recent thoughts are that Project Emerald is actually two phones from HTC, ie. the HTC Desire HD (myTouch HD on T-Mobile) and the HTC Vanguard/Vision (G1 Blaze or G2 on T-Mobile). They will be released closely following each other, and will be T-Mobile's first foray into the HSPA+/3G+/next-gen mobile broadband market.
It is possible that the HTC Desire HD is a completely different phone. According to the leaked roadmap, HTC Emerald will be coming out in November (quite separate from the HTC Vanguard that is supposed to be released in September). TMoNews thinks that HTC Emerald is in fact the myTouch HD. The codename for the original myTouch 3G was Sapphire, also a precious gem. Here is the real news though. It has a front-facing camera. It is unclear how large the screen is, but larger than a Nexus One (3.7 inches) and smaller than 4.3 inches. No word yet on the version of Android, though to be competitive, it has to be 2.2 or higher. It will run with the Espresso interface and have the genius button found on the myTouch Slide.
There is some speculation that the G2 will be a true successor to the G1. Namely, it will be a vanilla Android experience. It seems that it might also have a front-facing camera, 4.3 inch screen, and QWERTY slide keyboard.
It is unclear as to which processor(s) these phones will have, but there is speculation hope that it is a dual-core 1.2 GHz Snapdragon from Qualcomm. If it does actually launch in November, there is a good chance that it is in fact that dual-core beast.