I have been using Vim over ssh with my Nokia N900 not-so-smart-phone, and it works great compared to anything else I can think of. The phone has a physical qwerty keyboard but it does not have all the non-alphabetic keys you'd want and esc, ctrl and some other keys are accessed via touchscreen.
I have made some key mappings in Vim to get my non-US native keyboards keys that are normally not used in coding do something meaningful. I have ö and ä mapped to curly/square brackets, å is another escape and 0 and + (next to each other on the number row) are home and end. This makes it pretty convenient to write code on a qwerty keyboard and it also works nicely with a laggy phone internet connection over ssh.
I had a N900 and used to write lots of code in nano. It had python, ruby and PHP and was a great tool for quickly coding ideas or scraping and grepping web APIs. It ran vi and emacs too but I never really used them.
Now I have an Android device that's 5x faster and 10 more usable as a phone but I've only written about 10 lines of code in total on it's virtual keyboard. Hoping my next phone combines the best of both worlds.
I have made some key mappings in Vim to get my non-US native keyboards keys that are normally not used in coding do something meaningful. I have ö and ä mapped to curly/square brackets, å is another escape and 0 and + (next to each other on the number row) are home and end. This makes it pretty convenient to write code on a qwerty keyboard and it also works nicely with a laggy phone internet connection over ssh.