If you’re thinking about switching your wireless service and you’re a Costco shopper, now might be the perfect time to make a move. T-Mobile has rolled out a new in-store promo that could get you up to $450 per line—but you’ll need to act fast and meet a few requirements to cash in on the deal.

As reported by The Mobile Report, this limited-time offer is available at select Costco locations when you activate a new account with T-Mobile. The offer gives $300 per line as a virtual prepaid Mastercard, plus an extra $150 per line when you bring your number from another carrier (also known as porting in).

This means you could earn a hefty $450 per line if you’re switching from another provider and activating new lines on a qualifying plan. Just keep in mind: the full amount is only for customers who meet both conditions—new T-Mobile account and number transfer.

The promo runs from June 13 to July 3, and it’s only available at participating Costco locations, so it’s best to call ahead or check in with your local store. Customers must also stay on the eligible T-Mobile plan for at least 90 days to get the full value of the rebate.

If you’re already a Costco member and were planning to switch carriers, this could be one of the better deals to check out this summer. Just be sure to read the fine print, make sure your line qualifies, and don’t wait too long—offers like these tend to go fast.

Source: The Mobile Report