Apparently, Cisco does not support connecting one IP Phone to another through the PC port. Each phone must be connected to a switch port directly. If IP Phones are daisy chained using the PC port, they will not work. You can, however, daisy chain two Cisco Unified IP Phones - Expansion Module 7915s or 7916s - to provide 48 additional lines. Read on from www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/7_0_1/ccmsys/a08ipph.html.