Sending text messages on cell phones which only contain the keys 0-9 and \# and
* can be a painful experience.  We consider the problem of designing an optimal
mapping of numbers to sets of letters to act as an alternative to the standard
$\{2\to\{abc\}, 3\to\{def\}\ldots\}$.  Our overall goal is to minimize the
expected number of buttons that must be pressed to enter a message in English.
Some variations of the problem are efficiently solvable, either by being small
instances or by being in \ensuremath{P}, but the most realistic version of the
problem is \NP\ hard.  In order to prove \NP-completeness, we describe a new
graph coloring problem {\sc UniquePathColoring}.  We also provide numerical
results for the English language on a standard corpus which describe several
mappings that improve upon the standard one.  With luck, one of these new
mappings will achieve success similar to that of the Dvorak layout for computer
keyboards.

This also includes the code required to get our numeric results.
  make all
will make the article.pdf and compile all the .cpp files 
  make data
will generate all the data files (this make take several days, and I recommend
make -j data in order to use all your cores)

Submitted and accepted.  boothe.pdf is the paper and slides/talk.pdf is the
talk.