ISDN Costs: 
4/1/98
Connects per hour Minutes per Connect B-channel Charges: Total Per DAY: Total per Month
Business Hours: 

9 hrs a day

4x 2 1st min: $0.0333 
Additional min: 
$0.0105
1st min: $1.2321 
Additional min: 
$0.3885 
---------- 
$1.6206
$46.618
Off Hours: 

15 hrs a day

4x 2 120 mins (2hrs) free usage used per day 60 hrs of free usage used 
(120hrs remaining)
 
Pacific Bell has an interesting ISDN tarrif.  Check out the tarrif out to better understand this cost table.