Buy a 8000 yuan mobile phone with China Merchants Bank credit card and choose to pay by installment. The down payment needs 2500 yuan. If the installment rate is 3%, then the handling fee for each installment is 3% of 8,000 yuan, which is 240 yuan. If 12 installments are repaid, the total handling fee is 240 yuan times 12 installments, totaling 2880 yuan.

Therefore, after the down payment of 2,500 yuan, the remaining 5,500 yuan is paid off in 12 installments, and the repayment amount in each installment is 5,500 yuan divided by 12 installments, plus the handling fee of 240 yuan in each installment. The specific installment plan and interest rate need to be confirmed with the merchant or China Merchants Bank Credit Card Center.