Yevette,
The PRI basically has two parts to it. The T1 which is a "pipe" connecting the PBX to the Central Office Switch and the PRI or Primary Rate Interface with a defined set of functions and protocols that define how the two switches "communicate" and what features under mutal agreement(tariffed rates) will be active, ie. multiple CID. What I think your phone company is saying and not too clearly, is that your Primary Rate Interface needs to be upgraded to one that allows mulitple caller ID's. This is done in the PBX and or the CO switch. A new PRI T1 is usually built to allow for testing between the two switches before cutover.

Forty six years and still fascinated with Telecommunications!