I have had the droid X for 1.5 years. Just started having the "silent call" problem the other day and have had it multiple times between then and now. It doesn't seem to be associated with any of the activities that you have mentioned here. I have no solution but I do have more details on the problem:
- problem erratic (silent then fine then silent)
- doesn't happen mid call
- isn't associated with any one app
- resetting the phone always works (had success no 5 times)
- all other functionality still works
- makes call to other phone
- problem includes: can't hear other person and person can't hear you
- problem doesn't change when using headset, bluetooth, speaker, etc.
- haven't found any solution
Please help!!!