A first carrier may support inbound roaming requests for subscribers of a trusted second carrier. For example, the first carrier may receive an inbound roaming request from a UE. The first carrier may determine a second carrier that is a home carrier of the UE is a trusted carrier associated with the first carrier. In response, an IMS procedure associated with the UE may be performed including communicating, by a first CSCF node of the first carrier, with a first HSS of the second carrier, using a same protocol as used by the first CSCF node to communicate with a second HSS of the first carrier and communicating, by the first CSCF node, with a first AS of the second carrier, using a same protocol as used by the first CSCF node to communicate with a second AS of the first carrier.