TOYOTA 2011 Sienna - Manual (Page 572)

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3-5. Using the hands-free phone system (for cellular phone)
■ Call history
Up to 5 phone numbers can be stored in each of the outgoing and incoming
call history memories.
■ When talking on the phone
● Do not talk simultaneously with the other party.
● Keep the volume of the received voice down. Otherwise, voice echo will
increase.