For PRI utilization alert, here is what you can do login to your CUCM through RTMT and go to System-->Performance
you can see your call manager servers listed here, now choose the one on which your gateway is registered, you will get a big list of parameters here to choose, now click on callsInProgress -->right click on this and now choose an option
Counter instances-->choose your H.323 gateway and now you can see that there will be a graph created with current calls information in RTMT
right-click on the graph now a new tab will get opened called Alert properties, give a description and recommended action and click next, here you can set up a threshold for example if the callsInprogress exceeds certain number it will send you a notification from RTMT to your email.
For monitoring a specific interface (D channel), you might want to use an SNMP monitoring tool and you might want to enable SNMP traps for interface status change.
check for ISDN SNMP traps in this doc, it will give you an idea on how to configure it.
Hope this helps