It looks like DDTM was configured on Instinct to prevent applications from locking up due to time-out issues if a phone call were to interrupt data session. But in doing so, they made your cellphone useless if you were to ever watch TV on it because you would not receive incoming call at all!
So people found out that you can toggle DDTM setting and your phone will indeed receive phone calls during an active data session such as when watching TV. But on some occasions, this might lock up the phone. Personally, I would still like to see an Incoming call even at the risk of locking the phone up (which is not frequent anyways). My suggestion to Sprint is to make this an option in Settings in the next phone software update so people can set it up based on personal preference instead of outright blocking it completely. If this is not done by Sprint, then your only choice might be to take the risk of messing up your phone (it is pretty straight forward actually!) and do it yourself.