What is the difference between VoIP, CTI (Computer Telephony Integration) and IP telephony?
VoIP is going to be voice-only. You add telephony -- either of the last two -- and you add things like text, fax and other services that are not available to voice-only. It also will provide you with a far better ROI -- in particular you have many automation possibilities with a fully integrated system. The options are especially attractive if you add universal messaging.