Mentalist:
The main problem is the lack of a framebuffer in the stock kernel(or power kernel, for that matter); with that, it'd simply be a matter of running "/bin/sh", and there you go.
Without it, however, I'm stuck using text2screen to print characters, and evkey to get keypresses. What I did with my limited command-line interface was have an "input box", which was then run through eval. It worked... sort of. But as a run-command box, and not a terminal.