https://www.cnet.com/news/apple-ios-11-2-update-adds-apple-pay-cash-faster-wireless-charging/

Apple's new iOS 11.2 software update went live Saturday, adding Apple Pay Cash and faster wireless charging to supported iPhones.

For anyone with an iPhone 6 or later, the update's Apple Pay Cash feature opens up the ability to send cash to friends and family over iMessage. While I didn't see the feature immediately turned on after updating my own iPhone to iOS 11.2, when it does appear it should work similarly to Paypal's Venmo service.