If you have done these things are are still getting device full errors you have a faulty phone. It should have been exchanged for you the first time with no argument.

As a backup, take a printout of this thread with you. Explain that the community here knows a huge amount about the N900, and that Nokia developers of the *firmware* and *applications* are frequent contributors. And that if this community says the phone is broken, it is -- and the reason this thread was this long is that the community hates to give up until such is proven.