Not that this helps you much, but back in October when PR1.3 was released, I tried to do it over-the-air and it failed. I hooked it up to Ovi Suite on my pc and it worked just fine. I know you don't have a pc, but you should try to get to one if you can, download Ovi Suite (free) and try that.

Knowing that Nokia cut the ropes to the N900 last year, I wouldn't be at all surprised to find out that PR1.3 isn't on their OTA servers anymore.

Good luck!