The authentication code is required when subscribing a phone to a
network. It prevents other phones subscribing to the network without
your approval. Contact your network administrator for this code.

Call back

Some networks call you back when you for instance transfer an external
call to another phone without waiting for an answer but the third party
does not respond. The reasons for call back depend on the type of
network.

DECT

Digital Enhanced Cordless Telecommunications (DECT) is a digital
access technology which ensures a sound quality equal to that of a fixed
phone and provides maximum privacy. Eavesdropping or breaking in on
the line by strangers is virtually impossible.