The first confirmed device to support Managed Direct3D is the Dell Axim x50v. See the announcement.

Any Dell readers out there who want to let me into the beta testing program? I already have the hardware so it won't cost you anything.

There is some speculation on my part. Though it looks like Dell will upgrade the entire x50 line I am guessing that only the x50v will support D3Dm since its the only one with the GPU (see Dell Comparison chart - scroll down to highlights). Here the spec on the chip that dell use. For those of you interested Tom's hardware has an article on that chip (it has its origins in the Sega Dreamcast - fascinating). The competition is the ATI Imageon 2300 and NVidia GoForce 4800/4500 competition. I'm not sure which handhelds have the competing chips in and will have WIndows Mobile 5.0 support so for now its just Dell to look forward to.