If you’re looking to deliver content on a wide variety of mobile devices then the best advice I can give is not to use any JavaScript library. They’re largely untested and size will definitely become an issue across slow mobile networks.
Your best chance of getting anything working is to use JavaScript and the DOM without any abstractions; this will allow you to target and rectify issues directly.
PPK has a bunch of mobile compatability tables that might interest you: http://quirksmode.org/m/table.html
ps. If you’re only looking to target the iPhone then jQuery will probably work; still I wouldn’t suggest it…
pps. Developing websites for a wide variety of mobile devices is tricky business; the best thing to do is go back to basics and build up from there.