Siemens 300Series User Manual page 157

The other party cannot hear you when you are using the
speakerphone, though everything else works.
Verify that your telephone is equipped with a speakerphone (speaker
and microphone). Check the telephone name on the label underneath
the telephone. RP312, RP312L, RP612, RP612L, RP624, and RP624L
do not have microphones, and you must use the handset to speak to the
other party.
The telephone does not ring when called, though everything else
works.
Verify that the telephone is not forwarded. If the telephone is
forwarded, the line key flickers. See "Forwarding" on page 5–1 for
information on forwarding and cancelling forwarding.
Also verify that the telephone is not in Do Not Disturb mode. To cancel
Do Not Disturb, press the Do Not Disturb (DND) key until its status
light turns off.
Your speakerphone turns on and off when the other party is
talking.
Noisy environments may cause the speakerphone to behave as if you
are talking, thereby cutting off the other party. If you cannot eliminate
the background noise, try using the Mute feature while the other
person is talking, and then de-activate it when you want to talk to them.
(See "Muting the Speakerphone" on page 2–14.)
Help! B-3