In the end, what I'd really like is for a future iPhone to provide a standardized way to add lenses, such as via a bayonet mount (as has been rumored to be in development). This would allow you to use the same lenses across iPhone upgrades. Even better would be an iPhone with a built-in optical zoom. However, I believe such a lens is currently not possible without being unacceptably bulky. Still, with all the people who seem to be happy using their iPhone as their main camera, it's not out of the question that the situation might some day change.
Sign up for CIO Asia eNewsletters.