A non-MNO PSP network maintains a table that maps external subscriber identifiers of UEs to intermediate subscriber identifiers of the UEs on an interface between the non-MNO PSP network and NHN(s). The non-MNO PSP network obtains an SCEF-related message including either an external subscriber identifier or an intermediate subscriber identifier for the UE. Using the table, the non-MNO PSP network forwards the SCEF-message to a serving NHN or to an external application. In another embodiment, an NHN maintains a table that maps internal identifiers of UEs within the NHN to intermediate subscriber identifiers that identify the UEs on an interface between the NHN and non-MNO PSP(s). The NHN obtains an SCEF-related message that includes an intermediate subscriber identifier or an internal identifier for the UE. Using the table, the NHN either processes the SCEF-related message within the NHN, or forwards the SCEF-related message to a non-MNO PSP outside the NHN.