8255.mobi will be ok because it is not a bad number regardless of what it spells. I would be wary of registering long number words though, as the problem is that it is not intuitive to spell in numbers when using domain names, and the cost of educating the public is likely to be huge.
I got a couple, but only 4 number ones where the numbers are good on their own, e.g. 2277.mobi (car/bars; but more importantly just a good number!)
I do note that someone has registered 3569377.mobi (Flowers!)

hone: