Sorry for the delay in my reply...

1. Phones swapped out with new units (IX 5900 & IX5910)
2. PBX software updated
3. Phones Firmware updated
4. Phones A/C adapters swapped for PoE injectors
5. Phones had their IP addresses made static twice using 2 different IP addresses (in and out of DHCP scope)
6. Phones split off so they are independent of the computers
7. Phones moved to managed switch were PBX is connected to.
8. Replaced all patch cords at desk and patch panel.
9. Moved phones from 1st to 2nd floor (change location)
9. Verified with ISP that their hardware and configuration have not had any interrupts on their end.

What is odd, is someone can be on the phone and there is no interruption in conversation until the phone reboots.