[hcarvalhoalves]

If you need a short code the user will have to type the legibility is more important than the length, you can optimize for human input like this:

https://gist.github.com/hcarvalhoalves/5330d8af36e7163d58c4

[underwater]

You still need to remove '5' and 'S'. I'd like a to see people use similar algorithms for mobile input. The two most important characteristics would be to be purely lowercase and to cluster numbers and letters to minimize keyboard switching.