Toyota 2007 Prius Owner's Manual page 190

You can do this operation when you want
to operate an answering machine or use a
telephone service in bank for example.
You can register the phone number and
the code number in the phone book.
190
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D
Sending a tone by the speed tone
You can send a tone by the speed tone.
(For registering the speed tone, see
"Registering the speed tone" on page
195.)
1. Touch the "Speed Tone" switch.
27p212
2. Touch the desired switch to send a
tone.