Steps:

1. Power on the car to IG-ON or READY. IG-ON will do for this purpose.

2. Using the Trip/ODO button, set the Trip/ODO display to ODO (not Trip A or Trip B)

3. Power off the car.

4. Now power the car to READY (brake on). This is required so that step 6 works correctly.

5. Within 6 seconds of powering on, press and hold the Trip/ODO button for 10 seconds or more.

6. WHILE STILL HOLDING ODO *after* the 10 seconds, shift the “gear”
selector from P to R, then back to P. Now release the Trip/ODO button.
7. If the last step was successful, “b on” or “b off” should be
displayed in the location where the Trip Odometer or Odometer is
normally displayed. “b on” is beep on, and “b off” is beep off.
8. Press Trip/ODO to toggle the mode.

9. Now power the car off to exit the toggle mode.

10. Power the car on to READY and confirm the reverse beep status by
shifting to R. The beep should not be audible if “b off” was selected,
and should be audible if “b on” was selected..

Note: The Repair manual page states that if the the 12v battery is
disconnected, the beep will reset to the default of on, and this
procedure will need to be performed again. The repair manual also isn't
clear that Trip/ODO should remain depressed while shifting.

Additional Note: The driver and passenger seatbelt reminder chime can
be disabled or enabled (respectively, defaults appear to be driver on
and passenger off) using similar steps. Instead of shifting from P to R
to P in step 6, simply buckle then unbuckle the appropriate seatbelt
while continuing to depress the Trip/ODO button. There is one caveat to this procedure. No one can sit in the passenger seat while attempting to complete this task.

http://cellphones.about.com/b/a/052507.htm

I like the phone and it was very easy to set up with my 2004 Prius and
the hands-free works great. I paid $199 and then could have received a
$100 rebate

http://www.sprintpcsinfo.com/modules.php?name=News&file=article&sid=582

but I opted for the $150 rebate from Sprint because it was my first new phone in over 18 months.

I have two issues with using Bluetooth. About 30% of the time when I
make a call from the car it doesn't go through the first time.
Everything appears to be fine but there is no sound. If I hang up and
try again it always works fine the second time.

The other thing is that I still haven't figured out how to sync the
phone book on my phone with the car. I followed the directions in the
Prius manual but at a certain point it tells you to send the data from
the phone and I just cannot find any option on my phone for sending
data. I've tried making it discoverable and many other options but
nothing seems to work. Sprint technical support is absolutely clueless
about this phone.

Here's a site that describes the navigation system.