Well,if anyone has been following along (or cares for that matter)
found a BLUETOOTH headset that plays nice w/both phone calls & audio playback:
Sliver II Bluetooth Headset by Motorola - A Google Company
In a nutshell,I tested no less than 5 B/T's & cross-checked w/5 different phones & this was the only one that works well w/my T-MOBILE HTC ONE.
I was actually able to duplicate my issues on another T-MOBILE HTC ONE,so,even if not widespread,there is definitely something going on with B/T & T-MOBILE's variant of the ONE.
As awesome as this phone is,it was equally frustrating to not fully enjoy/utilize the B/T features w/o the party on the other end complaining/hanging up due to atrocious call quality.
To say that I'm glad to have this issue in my rear view mirror would be a gross understatement.
Now,perhaps I won't be looking too hard at the "NEXT BEST THING" on the horizon.....