I completed an upgrade of a demo 3cx version 8 windows based PBX today. Main things that impressed me were the speed of the upgrade – a few minutes and the ease of backing up the config and restoring using the wizard. The system was back up and operational in a few minutes. The main reasons for the upgrade were to get to the latest release for some more development and testing work – a client is interested in implementing it this year. The main thing I gained was a new version of the software phone client (looks like an iphone) which can allow you to have integration with your crm / contacts – in my case the upgrade works with Outlook 2010.
If you are interested in a PBX that is relatively simple to setup and maintain (and runs on Windows) check out the free version at www.3cx.com – I have mine linked to a voip provider and am planning some analogue integration as well as some more esoteric work as part of the planned project.