Or add the unlimited minutes add-on for $20/month It will be pro-rated based on how many more days are left in your billing cycle.
I would then remove it when your billing cycle ends. And when my minutes reach the limit again in the future I would add it back on again. This way you never pay the full $20/month. Only when you have reached your minute limit.
However you need to be very mindful of how many minutes you use