First thing i did with my iPhone was to see how my site looked on it. It was too heavy for it and the browsing was fairly uneasy. So guess what? I made it a priority to optimize Orkut Plus! to look best on iPhone and (very soon) on all-other mobiles.
I am sure iPhone users will feel it pretty easy and light to browse the site since the navigation is completely ajaxed and very fast and simple.
On other mobiles, the site looks fairly easy to browse on opera mini, but i can assume it will be very heavy site on other browsers and can incur lots of downloading charges while you are on mobile. I am planning to create a all-mobile optimized version of Orkut Plus! so that even mobile users can enjoy fast and quick navigation on their cell phones.