I3 is Interactive Intelligence. They license their call center product as a stand alone ACD, or partner with other manufacturers.
Here is a link to their datasheet.
I am not making any judgement about the product, but if I were you, I would spend some time evaluating the interoperability of your telephone sets with the product.
For example, do the agents have to use a PC based "softphone" to log in and out of the system, or receive call queue alerts? When calls are transferred out of the agent group, do they still display information on the Definity LCD phones?
Also, the Definity PBX has a 99.9995% reliability rating. If this system runs on NT or 2000, you can achieve acceptable reliability, but you will need to buy server hardware with redundant processors. Check the hardware and networking requirements for any client PC based features as well.
Also check the system limitations. One of the annoying characteristics I have seen with "Next generation" telephone systems is a datasheet that states "unlimited" call queues, simultaneous logins, etc. "Unlimited" resources is technically impossible unless the system is God. Check references from Interactive Intelligence customers who have integrated with Definity and have similarily sized call centers.
Above all, do not be pressured into a hasty decision. Your Customer will hold you responsible for the reliability and functionality of any system you install for them, even if it was their "great idea". Robert Harris
Communications Advantage