A list with certified SIP Service Providers (ITSP) can be found in G-DMS document INF-13-000534. The Wiki from Unify can also be used as reference that contains some of the infor­mation provided by the Service INF: https://wiki.unify.com/wiki/Collaboration_with_VoIP_Providers_on_Enter­prise_Platforms

In case a hardware exchange is considered, please refer to Chapter 3, “Board Replacement”