You're a 1P but have no 500 mile certificates in your electronic bank?

You have to buy them in books of (4).

You can certainly use your 1000 mile upgrade from the MP Visa.

You can use miles (15,000 --- a waste on such a short flight).

There are other certificates, such as time-verified upgrades and paper 500 milers, but those aren't things you're likely to come across in normal travel and not available for purchase. You might find them over at coupon connection.

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More Room Throughout Coach: the Website of Free Miles and Free Markets