Well, I already paid the first invoice when I bought the Sim itself, and it's being shipped to me, and I'll get it activated once it arrives, but you can also use something like T-Mobile prepaid as they have gs for it on coinsbee.com. That's what I've been using up until now and the reason I'm making the switch is because I want to be able to pay my phone bill directly with Monero instead of having to buy a gift card and then pay it with the gift card. So it just takes one step out of the process.

If your phone is newer than mine and supports Esim, you can have the service almost immediately. I actually have to wait for a physical Sim to be shipped, because my device doesn't have Esim support.