Many people seem to be afraid of mixing stable with testing, but frankly, testing is fairly stable in its own right, and with proper preferences and solution checking, you can avoid the "stability drift" that puts your core packages on the unstable path.
"Testing is fairly stable??", you ask. Yes. In order for a package to migrate from unstable to testing, it has to have zero open bugs for 10 consecutive days. Chances are that, especially for the more popular packages, somebody is going to submit a bug report for an unstable version if something is wrong.
Even if you don't want to mix the environments, it's still nice to have the option there in case you run into something that requires a newer version than what is in stable.
Here's what I recommend for setting this up:
First, create the following files in /etc/apt/preferences.d:
stable.pref:
# 500 <= P < 990: causes a version to be installed unless there is a
# version available belonging to the target release or the installed
# version is more recent
Package: *
Pin: release a=stable
Pin-Priority: 900
testing.pref:
# 100 <= P < 500: causes a version to be installed unless there is a
# version available belonging to some other distribution or the installed
# version is more recent
Package: *
Pin: release a=testing
Pin-Priority: 400
unstable.pref:
# 0 < P < 100: causes a version to be installed only if there is no
# installed version of the package
Package: *
Pin: release a=unstable
Pin-Priority: 50
experimental.pref:
# 0 < P < 100: causes a version to be installed only if there is no
# installed version of the package
Package: *
Pin: release a=experimental
Pin-Priority: 1
(Don't be afraid of the unstable/experimental stuff here. The priorities are low enough that it's never going to automatically install any of that stuff. Even the testing branch will behave, as it's only going to install the packages you want to be in testing.)
Now, creating a matching set for /etc/apt/sources.list.d:
stable.list: Copy from your original /etc/apt/sources.list. Rename the old file to something like sources.list.orig.
testing.list: Same as stable.list, except with testing.
unstable.list: Same as stable.list, except with unstable, and remove the security lists.
experimental.list: Same as unstable.list, except with experimental.
You can also add a oldstable in sources.lists.d and preferences.d (use a priority of 1), though this moniker will tend to expire and disappear before the next stable cycle. In cases like that, you can use http://archive.debian.org/debian/ and "hardcode" the Debian version (etch, lenny, etc.).
To install the testing version of a package, simply use aptitude install lib-foobar-package/testing, or just jump into aptitude's GUI and select the version inside of the package details (hit enter on the package you're looking at).
If you get complaints of package conflicts, look at the solutions first. In most cases, the first one is going to be "don't install this version". Learn to use the per-package accept/reject resolver choices. For example, if you're installing foobar-package/testing, and the first solution is "don't install foobar-package/testing", then mark that choice as rejected, and the other solutions will never veer to that path again. In cases like these, you'll probably have to install a few other testing packages.
If it's getting too hairy (like it's trying to upgrade libc or the kernel or some other huge core system), then you can either reject those upgrade paths or just back out of the initial upgrade altogether. Remember that it's only going to upgrade stuff to testing/unstable if you allow it to.
EDIT: Fixed some priority pins, and updated the list.
Just for clarification Hylafax uses converters in order to transform various types of MIME content find in mails to Postscript format, which BTW is the only format that can handle to send fax.
You can find the converters in the /var/spool/hylafax/mimetype/ directory in a default install. For example for the text (or plain) MIME type you will see there is a file called :
text/plain
or
text/text
With the contents of the command to be executed in order to transform the text file to PS.
The error you find is with the textfmt command executed in one of those files, so the problem can be solved by giving the correct arguments to the command line you will find in one of the aforementioned files ( man textfmt).
You can even use any other utility for converting from plain text to PostScript like a2ps.
Best Answer
We use Hylafax + Avantfax on a CentOS 5.3 virtual machine.
Incoming faxes are handled by our dedicated asterisk server using IAXModems. Each external fax no. has an IAXModem registered as IAX peer on the asterisk. The fax-server and the asterisk "talk" to each other using interceptty, which works surprisingly well. The idea was to keep the CPU-intensive tasks like creating PDFs away from our phone-server.
No hardware modem involed, but maybe this is still of some help.
Edit: Mix this with Avantfax and interceptty and you have pretty much, what we're using right now.