My guess: programming <i>on</i> phones is not common because text entry on most phones is optimized for text messaging- mostly just words. Entering punctuation marks is extremely painful on most phone (and tablet) keyboards. Even languages that are traditionally thought of as having sparse, simple syntax like Lisp need quite a bit of punctuation- parens, single and double-quote, and the question and exclamation marks are all important in Lisp.<p>Compare the touch keyboard of an iPhone to Graffiti on classic PalmOS and I think we've taken a major step backwards, albeit for a user scenario that is at best an edge case. The best feature of Graffiti was that it allowed a user to select a wide range of punctuation as quickly and easily as any other character.