There is a Garnet VM for N900, but the device will, of course, remain physically the same size.

It's a decent emulator, and completely usable, except that if it crashes -- and it occasionally does -- it takes all your data with it and starts over fresh. That's sad if you have a lot of data, because you can't sync it AFAIK. But having it was great, since I no longer needed to bring my Visor and my N900 along grocery shopping to use my favorite app: HandyShopper.