Reply to Nick,
If you work with kids teaching them to read phonetically (rather than
look-say), you'll discover that by and large, the phonetic rules work
very well. They'll pronounce about 80% of the unfamiliar words
reasonably correctly.
It "works" because they hear the phonetic pronunciation that they come
up with and realize that it sounds similar to (but not the same as!)
some particular word that they know. That clues them in that the word
it *sounds like* is probably the word that they're trying to read. You
can even hear them going through the process of starting with a
phonetic pronunciation and then morphing it into the real word.
(Besides, that remaining 20% is still quite a lot.)
I think that English can't be spelled phonetically because it isn't pronounced
consistently enough. Even if you spelled it 100% correct in the midwest US,
the south, southwest, northwest and east, not to mention the UK would still
be wrong.