I built something similar a while back (http://pagestackandroid.appspot.com/ if you're curious), for iOS I found that the easiest way to set up bookmarklets is to add them on the desktop (Safari or IE) and then sync to the phone. At the time bookmarklets didn't work on Android so we ended up making a native app (I think you have to register for the "share text" intent, it's been a while).