I have a few Tello lines. Most have less than $1 PAYGO balance for the past 2 years. One has $0 PAYGO balance for the past 2 years. None of those low balance lines have a plan. I've used the service on the ones with a positive balance about once or twice a year at most. All lines still have their phone numbers, including the one with $0 PAYGO, which I haven't used in 2 years due to the zero balance.
Your mileage may vary, especially if you don't hypermile like I do.