You can enable accounting or similar but it has a CPU impact . RADIUS is one option as it cannot send CDR to the UCM, but in a later version only CMR.
There is a call establishment rate type SNMP OID , but it’s not specific to which peer if you have many.
That’s as far as I’ve gone with it, the ISR G2 is far more sensitive to this sort of thing and will tank the CPU than Id thought