Vonage kept years of call records.

You might have 200 incoming calls taking you back 90 days for one customer.
You might have 200 incoming calls taking you back 3 days for another customer.

I vote for last 200 inbound and 200 outbound.
(After all, this is a residential service.)

You might offer 2000 calls for a monthly fee.
Unlimited call records for a higher monthly fee.
(People would need to opt-in.)