The present document defines the Terrestrial Trunked Radio (TETRA) system supporting Voice plus Data (V+D). It specifies: - the interworking of individual calls between TETRA networks; - the supplementary services interaction with individual calls between TETRA networks. The TETRA V+D interworking - basic operation part defines the interworking between TETRA networks over the corresponding interface: the Inter-System Interface (ISI). It comprises the following sub-parts: - Transport layer independent General design [2]; - General Design, PSS1 over E.1 [3]; - General Design, SIP/IP [4]; - Transport layer independent Additional Network Feature - ISI Individual Call (ANF-ISIIC) (the present document); - Transport layer independent Additional Network Feature - ISI Group Call (ANF-ISIGC) [5]; - Transport layer independent Additional Network Feature - ISI Short Data service (ANF-ISISDS) [i.8]; - Transport layer independent Additional Network Feature - ISI Mobility Management (ANF-ISIMM) [6]; - Generic Speech Format Implementation [i.7].