Is there a plan out there with zero monthly and paygo with use with a Smart phone - something like Tello PayGo for a phone like the S7 or S8?
Preference is either AT&T or Verizon service due to coverage.
ATT - there is truphone - 9c calls/text/mb but incoming calls and texts are free. Not good for data but otherwise decent since you can leave it for 6 months without any activity before you need to do something. They don't enforce the 6 month rule normally but obviously better to do it to be on the safe side.
Verizon - expo mobile - you have to pay $10 every 90 days but it is 2c a min/text. No data.
The US is unfortunately not set up for proper paygo. Tello started in the UK first so draws from what is the norm over there. No monthly top ups required, no to little expiry. Cheap rates.
If you need data you are best going with an annual plan from redpocket. $55 a year for 100mins/100 texts/500mb lte. Or look at tracfone or something like that.
h20 use att network, if seldom use data, it's 5c voive, text. $10 can last 90 days
Tracfone BYOP, which is 'kind of' PayGo, with a large top-up. Not as friendly, since you have to worry about both units & days.
Depending on usage, it can work out okay. Not good for ultra-low use of only a few units a month.
For example: buy one of the $60 bundles including roughly 1200 minutes, 1200 texts, and 1200 mb & a year of time.
Activate that phone.
Swap to a BYOP SIM for your preferred device & carrier.
Average monthly cost a little over $5. (including tax, maybe shipping)
If you use all of everything, and nothing more, it works out to about $0.0166 per unit. There are cheap add-ons for texts, reasonable add-ons for data.
Sell the Tracfone device to reclaim part of the investment, and get it down to $3.50 or so a month. .