Compatibility of 8x8 service with phones not bought directly from 8x8 depends heavily on one main factor: Does the phone have a valid factory-installed device certificate?
Certificate information is generally viewable within the phone settings under Status or Phone Status. If the answer is no, the device is not supported.
See the 8x8 Compatibility Matrix for a list of third-party devices that work with 8x8 service. In the case of Cisco and Polycom phones brought over from a different service, which are supported and have a valid factory-installed device certificate, be sure to factory reset the phone before provisioning.
Note: Accommodation of devices not purchased from or originally provisioned for service by 8x8 is on a commercially reasonable effort basis. These devices are not guaranteed to be supported on 8x8 service. DECT equipment supplied by 8x8 has been pre-configured and updated with software to support 8x8 service and 8x8 secure service activation. Used or refurbished DECT equipment or customer supplied DECT equipment is currently not supported for DECT service.