Seems to be all working now. After factory reset and using the APN settings from the site listed above, the last thing I had to do was, after clicking "Access Point Names" - on the next screen that names the APNs that I created: make sure the blue circle on the right is selected on the last APN that was created, the mms APN. That got picture texts and groups texts (MMS) working well for me. Hopefully that adventure is over!