You can use ui.convert_point((0,0),rootview,None) to get the screen position of the top frame. However, this has long been broken. in my uicomponents library, I had a RootView class with a replacement for this function. Quite honestly, never been tested on iPhone, but you might find it useful.
Another thing you might try: use convert_point to get the relative y of your textview relative to the root view. This does work. Then simply move the rootview.frame up by that y value. Should always bring the component in question to the top of the screen. For extra credit, account for the content_offset to keep the current line at the top.