I have nothing to do with development, but I can speak to the ability
for gears to work on the iPhone. Currently Safari on iPhone does NOT
allow for plugins. So with out behind the scenes cooperation with
Apple, NO this will not work in the near future. Google could develop
a Gears based app for Apples App Store, but Apple has been notorious
for not allowing competing applications into the App Store. A
"browser based" API would by definition compete with Safari.
If Google and Apple are working on something behind the scenes, I
doubt we will be hearing about it here until the companies make an
official announcement.