System → User Preferences → Call Hold Reminder → Tone Interval (secs)
N/A
<user_pref>
<hold_reminder>
<interval>VALIDVALUE</interval>
</hold_reminder>
</user_pref>
Set the hold reminder interval in seconds.
30, 60, 90, 120, 150, 180, 210, 240, 270, 300
30