Lexus RX 450h 2010 Owner's Manual page 401

3-4. Using the hands-free phone system (for mobile phones)
Call waiting
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If your phone does not support HFP Ver. 1.5, this function cannot be used.
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Call waiting operation may differ depending on your mobile phone and service
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provider.
Call history
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Up to 5 numbers can be stored in each of the outgoing and incoming call history
memories.
When talking on the phone
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Do not talk at the same time as the other party.
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Keep the volume of the incoming voice down. Otherwise, voice echo will
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increase.
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