This article describes some of the key affordances for learning of the generic class of handheld computers known variously as smartphones, palmtops, and thumbtops--using the Apple iPhone 3G as one of the most mature exemplars of this class--based on the authors' experiences with and reflections about the device over a period of a year. An argument is made that one of its most potentially powerful affordances is that of shifting the paradigm of educational technology away from providing learners with technological solutions ("development for learning") to that of encouraging learners to engage in interdisciplinary thinking about the design of software applications which are authentic and personally meaningful ("learner as developer").