It seems to me that one of the problems with Sprint Direct Connect ("SDC") is that it is not given the highest interrupt priority on the handsets. I'm not stating this as fact, I'm thinking out loud while trying to figure out why SDC works very well some of the time and is horribly unreliable other times.

What we have noticed is that any time our Kyocera Torques went to standby mode without first pressing the Home button, PTT calls can't reliably get through. If the last thing one of us did was read a text message, then set the phone aside and let it go to standby mode with the text application still "open", even when both phones have decent 3G signal, we consistently get the "user unavailable" #310 or #320 error messages, and PTT refuses to connect. Once we put the receiving Torque back to the home screen, THEN the PTT call can come through.

If I'm right, that is a major oversight on the part of Sprint/Qualcomm/Kyocera, because although PTT should not interrupt a voice call in progress, it certainly should connect a PTT call when the phone is idle, regardless if texting or some other application was the last thing open when the receiving phone went to standby mode. Requiring that a user always set the phone back to home screen to ensure that PTT calls will come through, is a real problem for PTT users and it should not be done that way.

Any SDC users having the same issue? I'm wondering how much of the lousy performance of SDC could be related to this oversight in terms of Sprint not setting the PTT interrupt level high enough. Or perhaps what I've described here is mere coincidence, and the real culprit is still Sprint's lousy overall 3G performance in many locales.