If you don't like the idea of one tag having multiple meanings, then it seems the best course of action is to use html-components to refer to the file extension. That tag is already being used for this purpose (by a few questions), and according to the MSDN article you linked, that's the full version of the name:
For Microsoft Internet Explorer 5 and later, HTML Components (HTCs) provide a mechanism to implement components in script as Dynamic HTML (DHTML) behaviors.
There's not much of an alternative for the smartphone brand, as HTC is now the official name of the company. It looks like it used to be "High Tech Computer Corporation", but they've dropped that. It's hard to imagine a better name for that tag.