It depends on exactly how you wish to set it up. If you want a “hosted” solution, then you would require a Telephony Gateway, a Data/Voice LAN. You would also require a ASP (Application Service Provider) to provide you a Predictive Dialer, CRM, T1s etc.
Alternatively, you can purchase all the hardware and have the solution hosted at your own end. This is good performance wise, but very expensive to setup initially. Not recommended for startup centers.