Comment 2 for bug 103705

Sure! First, add in your /etc/apt/sources.list a reference to debian source archive:
deb-src ftp://ftp.it.debian.org/debian unstable main contrib non-free
Choose another mirror if you prefer. Now, update apt index:
apt-get update
Probably you have to instruct apt to take the debian version (older than feisty's), to do so add this to your /etc/apt/preferences:
Package: sl-modem-source
Pin: version 2.9.9d+e-pre2-8
Pin-Priority: 1001
Now you can use module-assistant to build up your module:
m-a a-i sl-modem
On my system it compile and work, but sl-modem-daemon is very unstable. Probably you should backport it, too. To do this:
apt-get build-dep sl-modem-daemon
apt-get source -b sl-modem-daemon
I hope it works...

PS I don't have tried this because the computer wasn't mine, I have done it in a hurry..