Thumb Score: +63 T-Mobile is offering a $250 Prepaid Mastercard when you BYOD, Activate a New Line of Service and Port In a Number. Thanks AjayRajula Note, scroll down to "Current rebate promotions" and look for promo code 2020BYOD1 for details. You must complete port-in and register code within 30 days of activation; submit rebate using this form.