Now that we're in general discussion:
Download Vicibox.com's iso image. Install it on an old workstation. Use the PDF from the Vicibox.com site for installation. When that's installed, use the manager's manual from the Vicidial.org site to configure the system.
When you say you have a PRI, you're not clear on whether you are using it as a telephony connection to a telco or an internet connection (the predecessor to Broadband). If you have a 23-line PRI or a 30-line PRI (technology varies and I forget what it would be in India), your agent limit is based on the number of lines. Not on what the installer says.
However, if you are using the PRI for internet, then the bandwidth available could be a limiting factor.
In any case, if you're willing to pay them, they can limit you in any way they like as long as they disclose the origin of the software (Vicidial). It's Open Source, which means they must give you the source code. That does not inhibit their ability to contract with you for services in any model they choose. Note that they are offering support for a specific number of users. I hope you understand that the support load for a call center with 30 agents is somewhat different than it would be for a call center with 320 agents. LOL
That being said: Install it yourself. If it's easy, you don't need them. If it's not ... perhaps you do.