thejackalsg,
As you know, a CPC signal is a momentary drop in voltage which is used as a signal on the analog line which will normally have a small voltage when off-hook and a higher voltage when on-hook. If disabling DetectCPC fixes your problem it sounds like the Sprint Connect Box is issuing a false CPC signal when the OBi takes the line off hook. The Sprint Connect Box should give a CPC signal when the called party disconnects the phone and if the OBi cannot recognize the signal it can cause a port disconnect problem if the called party hangs up a call first.
The PhonePort has a minimum time for voltage loss to recognize the drop in voltage as a CPC signal. I believe the default time setting is 450 ms. I would try increasing that time and running tests the see if you can get a dial tone when you key # (with a higher minimum time setting). Then run some tests to see if the line disconnects if the called party disconnects first.
