There is no reason that Smartphone do not support Debian also.
This page is about to track every initiative to fully or partialy install the system on mobiles :
Smartphone taks is handled by FSO team :
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 :