When you think of “open source” do you only think of Linux? The fact is, there are thousands of software packages which are “open source”, and Linux is just one example. Another example is Asterisk – a completely free and open source PBX which runs on SUSE Linux Enterprise Server as well as many other flavors of Linux and Unix – even Mac OS X.
So if you’re in the market for an IP-based PBX, you might consider Asterisk as an option. Here’s an article from IT Manager’s Journal about how a car dealership in the mid-West US is using Asterisk for it’s enterprise.
It’s also worth mentioning that there is even a way to integrate Asterisk with Novell Identity Manager. A Novell partner has even produced a new open source project called VoiceRD (with available commercial support) that’s based on Asterisk. It includes Asterisk, SLES 10, and AppArmor security. They also offer some short, narrated screen cams of basic setup and administration to give you a flavor for what it’s like.