Can I switch USCellular Phone in contract to a unlocked phone

I want to purchase 4 line $90 plan which gives 4 free phones of $830 value (iPhone). I am planning to get those 4 iphones and I have to pay $90+ Tax for next 3 years. However I have zfold and zflip phones with me and they are unlocked. Does USCellular allow to switch the phones without loosing monthly credits for next 3 years?