Actually Homonyms already have that problem:

I tire easily.

The tire is flat.

You are thinking of homophones, which are spelled differently.  If we changed to a phonetic spelling all homophones would become homonyms:

http://en.wikipedia.org/wiki/Homophone

I'm not particularly good with foreign languages, but aren't spanish and some other languages strictly phonetic?  If so do they not have homophones?  

Right, thanks for the correction!

Interesting about the homonyms Kjeld, you are right, although I could argue that you can spell them all the same and you would need to determine meaning from the context.  This is what everyone has to do when they listen to someone speaking.  which raises the question, if one begins making changes would the primary focus be on clarity for spoken language or written language?

What was it called... from a while ago.... Esperanto?  I think that's it. The Focus was clarity for spoken language and less and less contextual meaning.  Which meant a much easier language to learn, and use. But less "beautiful" as the criticisms go.

Esperanto is old school.  The new hotness in constructed languages is Lojban:

http://en.wikipedia.org/wiki/Lojban

• It has a grammar that is based on predicate logic, designed to express complex logical constructs precisely.
• It has no irregularities or ambiguities in spelling and grammar (although word derivation relies on arbitrary variant forms). This gives rise to high intelligibility for computer parsing.
• It is designed to be as culturally neutral as possible.
• It allows highly systematic learning and use, compared to most natural languages.
• It possesses an intricate system of indicators which effectively communicate contextual attitudes or emotions.
• It does not have simplicity as a design criterion.

Doesn't matter what language you start with every group of people create or adopt slang expressions, or change the pronunciation of existing words over time.  Never going to have a perfect language without redundancy. It'd get f'd up in only a couple generations.  English is super flexible and annoyingly imperfect because it's three separate language roots jammed together.

I am sure the Borg could make an efficient and inflexible language - but, I agree, humans can not.