Yes, I have sufficient bars--at times, more than @Hook so that doesn't seem to be the issue. There has been discussion that an inconsistent band lock (bands jumping from 4 to 12 or whatever) may be the culprit, but I don't believe anything is definitive.
And I also don't believe that the OS choice has anything to do with telephony. Further complicating a found solution is that GSM is still available for TMo users (though next April, it's discontinued), so successful calls may hinge on a GSM default. Hook and I played with many scenarios, and other than his continued calling success, and m