As per SAV recommendations do not run Scheduled ( full scan) scan when call is processing.
Auto-Protect andDefinitions updates does not have any affect.
Makesure you ae using latest version of Call Manager as it has huge Bueffer Overflow any other vulnerabilities.
SEP has a firewall and IPS component called Network Threat Protection that might conflict will the devices however you will have to make MAC exclusions in the firewall to allow them.
or Simply do not install Netowork Threat Protection component of SEP.