Need help, Can anybody tell me which model of Sprint Sim does 306sh use?

Hi guys, I just bought used sprint 306sh and trying to use it with Ringplus, but the phone came without sim card. As I know Sprint has hundreds different sim cards for different phones, just try to buy the correct one and avoid losing money, can anybody tell me that which model of sim card is using on your 306sh?

Thanks a lot.

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