[T-Mobile Prepaid](https://prepaid.t-mobile.com/marketing-module/prepaid_plans.html) meets your requirements currently. Note that their offerings have changed over the years and may continue to change.

First, get a T-Mobile Prepaid SIM by going to a T-Mobile store in the US. They can get you started with "[Simply Prepaid](https://prepaid.t-mobile.com/marketing-module/simply_prepaid.html)" which is currently $50+tax for 30 days of unlimited calls/texts + 10GB data. You may have to pay extra for getting a new SIM.

Before the 30 days are up, log in at [https://account.t-mobile.com](https://account.t-mobile.com) to pay for the next 30 days. You add the money to a prepaid balance and then it gets deducted when the next 30 day period starts. Repeat every 30 days.

When you no longer plan to use the SIM but want to keep it active, log in and click "Plan" and change to "[Pay As You Go](https://prepaid.t-mobile.com/marketing-module/pay_as_you_go.html)" which is currently $3+tax for 30 days including 30 minutes or texts. The change will take effect for the next 30 day period. You have to add at least $10+tax to your balance, which will be deducted $3 every 30 days. You don't have to use the SIM at all, but I'd still suggest to log in and add another $10+tax at least every 90 days to be extra sure your account doesn't get deactivated. 

When you want to change back to the $50+tax plan, log in and click "Plan" again.

If you need to change plans and can't wait for the end of the current 30 day period, you'll need to add money to your prepaid balance and then call T-Mobile customer care by [dialing 611](https://support.t-mobile.com/docs/DOC-4041) from your phone and the representative will make the change for you. They can also help you with other options that aren't on the website like [$5 to add 500MB for one day](https://support.t-mobile.com/docs/DOC-7261), etc.