We've got one Linux box in the office. We have one boffin willing/able to learn Linux command-line processes (Yum, anybody? ;-) ) whereas I get by using Webmin. The server is a venerable PIII with 256M Ram that was effectively mothballed prior to this reincarnation. It runs our international pbx, e-mail/pop/fetchmail/spam assassin/procmail (meaning almost no spam reaches us), MySQL database, Samba, ftp server, Apache web server, contact management and a heap of other stuff. It works well and costs us essentially nothing (though we did decide to replace its original 20gig hard drive earlier this year.)

As for real cost, including our own time: the pbx has consumed quite a lot of time but that's because people like to tinker. The time to reinstall Linux from scratch and configure users/e-mail etc using the Trixbox distro is measured in low hours if you do Samba and Webmin first. We did that when we replaced the drive. Samba can be a bit tricky (because filenames are case-sensitive in Linux but not in Windows) but we've gotten used to that too.

We did it because we wanted a voip pbx and Linux is where it's at, but it's really opened our eyes to the possibilities out there. Certainly it was a real buzz to reincarnate the PIII rather than buying another server. FWIW the machine has not yet had to use swapfile meaning we haven't bothered to increase the memory. There are people out there running all this on fanless solid-state boxes the size of a dictionary. Look at http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120256922087 for an example; this one allows you to plug in 4 landlines and run a hybrid voip/pstn pbx as well as all the stuff above.