Benefits:
– Cisco requires 20% maintenance fee yearly from Cisco partner
– Cisco upgrade path is always expensive
– Voicemail system in Asterisk is better than Cisco Unity Voicemail. Cisco system voicemail administration is separate from user/extension administration. Asterisk combines device management, User, Extension, Voicemail, and Device configuration on one screen.
– Cisco phones will work with Asterisk. Going forward, new units can be bought from Polycom as the lower priced, yet comparable quality to Cisco
– Asterisk is open source, which makes it easy to integrate to any future in-house software development such as a call manager integration with Microsoft Dynamics
– There are many highly skilled Asterisk consultants in the USA market which would cost only a fraction of the Cisco contract
 
Disadvantages:
– Cisco can scale out to hundred thousands of devices with multi-site capability
– Although Cisco partner charges a high fee for support, they do have track records of good service