Provided that the network and the involved terminals support AMR-WB, the terminals will encode/decode using this algorithm.
The switch to “HD Voice” is automatic; no special handling to do, no special subscription needed. On the contrary, it is not normally possible to prevent this from taking place, and this is not signalled neither! Only the user’s ears will tell…
“Folding back” to narrow band takes place when one of the terminals is not compatible, and/or there is an interconnection with a non-compatible network (a noticeable example is the “wired” telephone network). So far there is no connectivity between competing operators or different countries. This will eventually be implemented, however.
