[Treo] Treo 680 Ring # Before VoiceMail?

[RECMSOJ]

   How do I set the number of rings the phone will deliver before
automatically sending the call to voicemail? I am currently in Mexico
and not only missing calls but unable to return them because it blocks
most caller ID's here. I can't find anywhere in the phone help (on the
phone itself) or on the website so far as to how to set this.
Thanks,
Dick
Richard E. Johnson, ScM, MD, DABA
[EMAIL PROTECTED]
Treo 680
Apple G4QS, G3 iBook, G4 PowerBook