While the Google Fi flexible plan is $20 usd/month, you can also suspend for up to 3 months when not using it. This post from their community seems to indicate you can suspend for up to 180 days total per year. Second post has a discussion about how quickly the number comes online after unpausing and indicates the number is live within a minute or two, probably like landing after a TATL. Second post also has commentary about using FI and GV now that they separated. GV free account is going away this year.
https://support.google.com/fi/thread...gure-out?hl=en
https://www.reddit.com/r/GoogleFi/co...y_with_new_gv/