When the tel URI corresponds to a circuit-switched user, the S-CSCF's query to ENUM will fail to resolve the tel URI into a SIP URI. The S-CSCF will then route the call to the circuit-switched network through an appropriate gateway.
In contrast, the possibility to concurrently assign an IMPU to multiple devices is a basic IMS feature, supported by the IMS core network (i.e. S-CSCF), without the need for a specific support in the application layer. The dynamic allocation of an IMPU to one or several devices is performed through the IMS registration procedure.