Insight into the ComConsult Study "Cycos mrs vs. Cisco Unified Communications":
"[...]Unlike Cisco, there are no artificial boundaries between different versions within the licensing model, making a change of version due to a rapidly growing number of users unnecessary. At the same time, the costs of acquisition for small and medium-sized companies in particular are very attractive. In typical scenarios, these amount to only about half the costs of a corresponding Cisco solution. In addition, small and medium-sized scenarios have much lower hardware requirements. This means that particularly when introducing Unified Messaging and Unified Communications with the aid of mrs, considerably lower hurdles have to be negotiated both from an economic and a technical point of view.[...]"
The complete comparison study between mrs and Cisco Unity is available at the following link as a PDF.