Kenwood TK255 User Instruction Manual page 17

Call from the PABX
This last display shows that the mobile is unable to determine the
calling party ident. The call may be returned however by pressing the
CALL button.
A special ident (not a mobile) which the Network uses.
If the call is not answered, (except in the case of PABX/PSTN and SPECIAL
idents, the ident of the caller will be put in the mobile stack.
The CALL symbol is used to indicate that there is one or more entries in the
stack. A pip tone is also generated.
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Fylde Microsystems Ltd - Kenwood User Instructions ver 0.09 Page