Number of PRIs Required

I have a customer that has about 200 phones and they gave me no information regarding call volume usage. When we started to install they created a huge Auto-attendant tree which I am sure will consume a great deal of time. According to Erlang B 23 lines on the PRI are available with .01 blocking and it gives me 14.45 erlangs offered. If each call is around 2 minutes, they would need to receive 300 calls at the busy hour to exceed capacity correct?