Just asking for best isn't enough. I use Ting.com and for my second phone I'm on a free FreedomPop SIM. I've had the FreedomPop for about 2 years and total cost over 2 years has been the cost of the SIM at 10 dollars. I carried both phones on a 3,500 mile road trip from San Diego to Vancouver Island BC, Canada and coverage was great. Besides Canada I only found service to drop 2 times. Once in somewhere in Pocatello Idado and a remote beach in Washington. In both cases, service came back on both phones when I walked back to a parking lot.
I found this article on CNET. I am trying to choose the best service for my needs.
https://www.cnet.com/how-to/apps-that-give-your-phone-a-second-number/
I can't tell for sure which services in the article are dependent on the internet and which aren't. I want to be independent of the internet. I would like to have calling and texting, including picture texting, and voicemail. I am using a Samsung S6, and currently using Cricket Wireless.
Burt

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