There is no reason that Smartphones do not support Debian also.
This page is about to track every initiative to fully or partially install the system on mobile ?phones :
Hardware
?OpenMoko : FreeRunner : http://wiki.debian.org/DebianOnFreeRunner
?Nokia : n8x0 (n800/n810) : see "Easy Debian" bellow
?Nokia : n900 : http://elektranox.org/n900/todo.html
?HTC : Nexus1 : http://www.android-devs.com/?p=152&cpage=1#comment-25
?Motorola : ?
Projects
Smartphone tasks is handled by ?FSO team :
http://wiki.debian.org/Teams/DebianFSO
Openmoko's FreeRunner is so far the ?device best supported :
Nokia's ?maemo is based on debian :
Same as ?mer the community based fork :
Upcoming distro ?MeeGo may be open to accept debian (re)built packages too :
Also there is an ugly alternative to install debian is to run it in a chroot dir :
http://wiki.maemo.org/Easy_Debian (instructions there are probably for Nokia n900, where as for Nokia n800 under OS2008, one may prefer : http://maemo.org/downloads/product/OS2008/easy-deb-chroot/)
http://ubuntuforums.org/showthread.php?t=1413313 (on htc nexus)