Global Travel Pass- when you get charged

I went to Japan and rented a portable Wi-Fi router to use with my daughter's and my Xfinity Mobile Phone because it is cheaper than the $10/day Global Travel Pass (GTP) or just using pay-as-you go data. I was kind of surprised when I got charged for a Global Travel Pass. In retrospect, I should have just shut it off for my trip. I want to pass along to others who might want to economize their Global Travel Pass usage. The $10/day charge started when I did the following:

-When I answered a call from the United States, it started the $10/day charge. My experience with other services is receiving calls is free, but making calls cost. Not so with GTP. Note that I had Mobile Data turned off.

-When I replied to a text message even with Mobile Data off, it started the $10/day charge. Reading text messages didn't start the $10/day charge. Note that I had Mobile Data turned off and was connected to hotel Wi-Fi.

By comparison, my daughter and, later, my wife, made calls and texts without GTP. In Japan, it was $0.10/text message and $0.50/min for calls, which was more economical than GTP given they didn't make many ($1.70 for 10 days for my wife; $5.50 for 10 days for my daughter). Note that we use the LINE app in Japan to call, video chat, message, in Japan.