Edit: Other post on this did not show up in my prior search for project fi. See first thread here: https://slickdeals.net/f/12372796-buy-any-project-fi-phone-including-pixel-3-and-3-xl-receive-a-travel-gift-card-of-equal-value?v=1&src=SiteSearch
Today only, purchase a new phone with Project Fi and get a gift card for Delta, Hotels.com or Southwest for the amount of the purchase (limit $999). Valid for current customers and new transfers. New customers MUST transfer in a phone number which has been in service since 8/28/2018. The phone must remain active on the service for 120 days or you will be charged the value of the gift card.
The rules do not specify it must be a mobile carrier, so I transfered in my Google Voice number.