This is something I've wanted to do, so let me share the random ideas I had:

- Horizontal space is at a premium, so don't show line numbers. When scrolling, show the line numbers hovering over the lines (so I can find my spot in a long file if I need to), but I don't need to see them while actually editing a line.

- The big win on the iPhone is not so much writing as reading. Make it easy to download a GitHub repo of source I might want to read on my commute. And make it easy for a project to link to that. Then I can get familiar with the coding style and abilities of, say, backbone.js or some other new javascript thing, while standing on the Metro.