Hi there,

So for starters, the ZTE Wireless home phone may not work on the frequencies that are supported in the US, and I don't believe they’re eligible to have the easy roam add on applied to the plan, as in, you cant use it in the states as it wont let you roam on their network. Only phones on a monthly plan and with the easy roam add on can be billed for international usage. As for the prepaid account, you can use the phone in the US as long as you purchase a US Roaming Booster and add it on your account. Some information on these can be found here https://www.koodomobile.com/en/help/long-distance-travel-and-roaming-prepaid under travelling with my prepaid phone. I hope this information helps 

Thank you