Hi Tim,
This can be changed on a line by line basis, have a look (in this instance maybe you would like the Ring Once option);
Device>Phone>Directory Number Configuration
Line Settings for this Device
Display (Internal Caller ID)
External Phone Number Mask
Line Text Label
Message Waiting Lamp Policy
**Ring Setting (Phone Idle) Use System Default, Disable, Flash Only, Ring Once, Ring
**Ring Setting (Phone Active) Use System Default, Disable, Flash Only, Ring Once, Ring
Hope this helps!
Rob