Previous, partly now outdated information on how to install Debian manually has been moved to Manual Debian.
To make suspend available you have to install apmd:
apt-get install apmd
After that you can suspend your phone with:
and make it wake up again with pressing the power button.
Wuth 06:28, 17 August 2008 (UTC): I found that apmd was already installed by using the official debian installation procedure, but that the kernel didn't support apm. I haven't yet resolved this issue.