I had a radically different concern than yours so had a radically different option that I chose. I am an expatiate living in Canada and USA cell rates for international were killing me.
Solution! Took some wrangling with AT&T but my USA cell number (under contract) is now billed as a gaming device, which effectively deactivates it, and I have s Canadian cell with unlimited CA and USA calling for $30 flat rate add on. USA cell rates are a ripoff by comparison.
My net ten phone has 9987 minutes left and I have 115 service days. I use about 10 minutes a month. I buy 6 months service with 1500 minutes for $100. That’s about $17 a month just in case I hit another deer. Earlier this year I was able to transfer about 9000 unused minutes (that I had racked up in addition to the almost ten thousand I have already noted above)to a new phone for my husband but he never used it and is now out of service days. I am not going to buy him more service days and we will waste all those minutes worth ten cents each.