ISDN PRI

My company just signed up for 60 months of ISDN PRI Full 23+ Call
Display: 5 year @ 877.53 per month and 25 DID's for 5 years @51.25.
My question is this:

Is there any special hardware required? We have a Norstar Modular ICS
Key Service Unit with Standard Softwar Rls. 4.1.1 and Startalk Flash
Voicemail, T M7324 Display Set, 1 T-7100 Display set and multiple
T-7208 Sets.

I am just worried that we are being underquoted and I don't really
understand the technology. Does anyone have any advice?

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