Binatone iDECT L1i System User Manual page 41

If the fault persists:
Disconnect all other instruments connected to the same line and try to
make a call. If this works, one of the other instruments may be faulty.
Disconnect the base unit from the telephone line and plug a different
phone into the master telephone socket. If this works, the line is ok.
If the call does not work and you are using a two-way socket adapter,
remove it and plug a telephone directly into the socket.
If the call now works, the adapter may be faulty.
If you cannot make a call, the fault may be on the exchange line, so please
contact the service provider.
This telephone is not equipped with a grounding function, and therefore
some of the functions may be limited when used in PBX systems.
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