I have several old dumbphones on Vodafone prepay plans (for various alerts and purposes), and as far as can see they have always and still require only $20 a year top-up to keep the number alive.

A month ago, I have placed a Vodafone SIM prepay card in a spare smartphone, and the use of that smartphone is supposed to be 1) to send and receive SMS when anywhere in NZ; 2) to access the internet at home only via wi-fi; 3) to be able to locate the phone outside of home using Google "Find my device"

I had credited the number with $20 and was hoping that it will suffice. I have sent 17 SMS messages (supposed cost: $3.40), and made no voice calls. However, I am now receiving a message via the "My One NZ" app that my balance is $9.40, it expires 3 Aug 24 (next year), I have 1.68GB of data left for 4 days until plan renews on 6 Sep 23.

So what happens if I don't renew that data plan in 4 days? Will my data simply be inaccessible outside of home, but the phone and SMS will keep working for a further 11 months until I top-up with another $20?

Would it actually be better to uninstall that "My One NZ" app from that particular smartphone?