One that hasn't been mentioned so far, non-free firmware (I believe)
but making use of the armel debian repos: Titchy Mobile on the HTC
Universal. (Yep! Debian on a phone!)
http://wiki.neilandtheresa.co.uk/Titchy_Mobile
which can make calls and send sms from the commandline, and receive
them via a whiptail dialog interface.
You can run X, and ppp over gprs/umts is also supported, according
the wiki
Wifi used to work, is now unstable, but will probably be fixed sometime.
Definitely an alpha environment, but fun! It's a sort of un-sponsored,
in-the-teeth-of-the-manufacturers effort. The handset is clunky and
unfashionably huge, but with a unique swivel-screen arrangement that
might tweak your tech-toy neurons :)
There are other linux images available for the Universal including qtopia,
http://linuxtogo.org/~htcpxa/htcuniversal/index.html
but development has severely slowed there.