We haven't heard a peep about any sort of successor to the HTC EVO 4G, but a recent trademark filing shows that HTC may have something up their sleeve.  As you can see in the image above, HTC's lawyers applied for the trademark "HTC EVO Shift 4G" last month.  There's no other information to go on at this point, although it's important to point out that before settling with the name "HTC EVO Shift 4G," the company originally filed for the name "HTC EVO 4G Shift."

Considering how hugely popular the EVO has been, and continues to be, it shouldn't come as a surprise that HTC would be working on a sequel to their 4.3-inch monster.  Unfortunately, we don't know much about the device, although it's probably safe to assume that it'll be running on Sprint's network.  Once upon a time, HTC released a UMPC with a hardware keyboard called the Shift, leading many to believe that the inclusion of the word "Shift" in the newly-trademarked name means that we'll be seeing a physical QWERTY-equipped EVO arrive.  Is that something any of you would be interested in?

Via Engadget, United States Patent and Trademark Office (1), (2)