The decision to implement VoIP should be based on the quantitative value it brings to the organization. It requires a thorough economic analysis taking into account:

• Objectives of the company

• The value the applications delivers to the business in a given time frame

• The risk level of the project

• Industry specific legislative imperatives if any (such as e911, privacy and or liability issues)

• Technology life cycle

• Existing infrastructure, applications and processes of the company

• Impact to the existing business processes

• Leverage existing assets of the company (to the extent possible deploy in stages, to mitigate risk)

• Scalable solution to handle increased demand

• Open hardware, software and protocols (multi-vendor solution) to reduce total cost of ownership

Solutions that have proven business cases include Contact Centers, IP Telephony, Messaging, Business Continuity Planning, Security

The resources above provide more information on how to do some qualitative and quantitative analysis for migrating to VoIP.