While at the Costco T-Mobile cellphone kiosk on Friday to activate the Pixel 3a phone I had just bought at Best Buy, I saw a notice that the T-Mobile BYOD Postpaid rebate was now $150 per line. I asked the salesperson about the rebate, which I thought was $50 a line, and he said it went back up to $150 the day before. The promo code for this rebate is T01273 and it is an online submission. The promotion dates are 1/24/20 to 2/20/20. The device must be active for at least 3 billing cycles. The printed material says that you should get a T-Mobile $150 Costco Shop card in about 14 weeks. Barring unforeseen circumstances, of course.
Store Locator: https://www.costco.com/warehouse-locations