I have a Mitel 3300MX controller ver 7.1.6.10_1 w/SP1. No trunked ports. Voice Vlan and Data Vlan are segmented. No PCs going through Phones. I have 5220IP phones and 5207IP phones. Problem is the 5207IP phones reboot (more than occasionaly) when on Speaker and or Conference calls. They don't go dark. They just ask for DHCP again. I've changed Switches and Power. I've upgraded software iuncluding re-format hard drive. No alarms on system. Any ideas?