Contract machine refers to the type of mobile phone customized by communication operators and mobile phone manufacturers. Users must sign a contract with the designated operator to pay the rental fee in one lump sum (mostly in the name of telephone deposit).
Generally speaking, the contract machine can't change cards. After changing the card, the phone bill will not be refunded, and there will be a penalty.
Despite these limitations, contract machines still have many advantages over bare machines.
The supply of bare metal in the market is not guaranteed, and the contract machine must be licensed, and for a long time after signing the contract (Unicom usually has two years), there is no need to pay or rarely pay the phone bill. In fact, users spend less money on the mobile phone itself.