Sort of true. It all depends on the environment- even on old hardware, even though it's more meaty than somethin like Damn Small Linux, if you have the right environment, it can still run with acceptable speed (Fluxbox and Ubuntu runs on 112 MB RAM).
So as long as the phone has a compositing-enabled video chip, it should be able to handle Ubuntu Mobile fairly well.
Full-blown Ubuntu, though? Hell no. XD