Motorola M900 User Manual page 61

The car radio must have a dedicated port in order for this feature to be
installed.
Once installed, the feature is always activated.
Loudspeaker Connection
This feature provides voice and sound connections through the car loudspeaker,
instead of the built-in M900 speaker.
The loudspeaker that is used for this feature must have an output of 4 ohms or
greater.
Once installed, the feature is always activated.
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