Most cell phone don't support a version of the Flash Player.
Many upcoming smart phones will support Flash Player 10.1 [not released yet] which will also suppor Flex Applications.
Many existing smart phones [not from Apple] have announced support for Flash Player 10.1 .
Anything before that will most likely support Flash Lite, if any version of Flash is supported at all. Flash Lite [as far as I knew] did not support ActionScript 3; and therefore will not support Flex applications.
I used to work with Flash 3-4 years ago and Adobe made such a big deal that you could test/simulate it on Nokias and Motorolas - I just figured the collective "we" had advanced since then.
It's hard to live in the future.
Back to HTML.