show logging is the command to see the logs in a router , you could check your logs and filter on the interface
you can increase the logging buffer with logging buffered xxx or else send them to a syslog logging host x.x.x.x
#sh log | i Interface Serial0/1/0:1
003461: Feb 15 10:42:11.461 UTC: %ISDN-6-CONNECT: Interface Serial0/1/0:1 is now connected to 2002 N/A
003462: Feb 15 10:42:17.841 UTC: %ISDN-6-DISCONNECT: Interface Serial0/1/0:1 disconnected from 4989930882112 , call lasted 6 seconds
003528: Feb 16 09:22:58.367 UTC: %ISDN-6-CONNECT: Interface Serial0/1/0:1 is now connected to 8251662 N/A
003529: Feb 16 09:28:20.945 UTC: %ISDN-6-DISCONNECT: Interface Serial0/1/0:1 disconnected from 704383812 , call lasted 322 seconds