If a company wants to outfit a call center, and if this is the large company, then it gets to take a "best of breed" approach, choosing the most appropriate components from multiple suppliers, and then hiring integrators to tie it all together. But small and medium-sized companies generally turn to full-service telecommunications resellers who offer complete call center systems from multiple manufacturers, or dedicated dealers who specialize in one manufacturer's offerings.
An integrated hardware and software packages are carried by these call center system vendors since the call center software is dependent on the phone system hardware. But you'll be pressured to upgrade your phone system in order to get access to the software features. You should be prepared for this.
Call center systems that are independent of your phone hardware are also offered by other providers. And this is almost always the case for hosted solutions. Some on-site vendors offer call center software that integrates with existing PBX systems or switches. Going this route, it is important for you to know which vendor is responsible for integrating the separate systems.
It is easier to connect to your existing databases than connecting to your phone system. You chosen vendor will analyze your situation and give you the specifics, but integration with SQL, Oracle, and other popular databases is usually straightforward.
Most vendors will show you the software in action that will give you better sense of the software. But you have to try to include someone from IT, the call center manager, and a "regular" agent in these demonstrations.
To log in to a sample account, you need to have a username and password, and online providers may give you these. This allows you to evaluate the system on your own without a salesman looking over your shoulder.
Of course, you want to spend not much money, thus, look into open source solutions that can offer the full features of proprietary software at dramatically lower prices.