Auerswald 461.2 - Manual (Page 87)

Appendix
87
No call number displayed
when a call is received Network operator or PABX
does not support the function
or function is not authorised.
The caller has suppressed his
call number or has a secret
number.
The call comes from a public
telephone.
The called is made via a
telephone network that does
not support transferring call
numbers. Check with network operator
or PABX as to whether
function is supported or needs
to be authorised.