How can I get a report on how many calls has been distributed (in and out) by the Call Manager?
you can use CDR Analysis Reporting (CAR). CAR generates reports for traffic, billing and QoS information. it can be found in CUCM Serviceability under the Tools Menu.
for further reading see http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/service/6_0_1/car/carovrvw.html
hope this helps