From a Martin Company press release:
To commemorate the Wind-up Records release of the original cast recording for “Walk The Line” chronicling Johnny Cash's life, Martin has created a limited production run of the Martin D-28 Special "Walk the Line - Original Motion Picture Soundtrack" Limited Edition. The guitar is a black D-28, labeled inside with the following:
"To commemorate the release of Walk the Line - Original Motion Picture Soundtrack. In memory of Johnny Cash 1932-2003".
The production run has been limited to only 12 units, and number 1 is to be presented to Joaquin Phoenix (the actor playing Cash in the film). The remaining 11 guitars will be given away through a variety of exclusive contests.