Focus Research Insight: How does the installed base affect VoIP evaluation?

Buyers' requirements, preferences, inhibitors, risks and even budget can all affect the way they progress through the evaluation process. How does your installed base affect the way you're looking at a new phone system? Are you more focused on specific integration capabilities? Cost savings relative to what you pay now? A similar user experience? [Improved] Vendor support/ service? How much of the evaluation revolves around the old system (and your experience in general), and how much is purely assessing the features and new technology?