Sprint and Google formally announced their partnership with Google for RCS messaging support in their Messenger app back in November, and at the time it was limited in what devices had support, including only a couple of LG devices and some Nexus devices on the network once they received the latest Messenger update. That changes today it seems as there is now at least one new phone that supports RCS messaging on Sprint through Google's Messenger app that wasn't mentioned in Google's initial announcement. This new phone is the Moto G4 Play according to Redditer 9710, who states that they tested RCS messaging on different phones with a friend, another Redditer named /u/Naturesbflol.
User 9710 also mentions that RCS messaging was working on the LG G5 , Nexus 5X, Nexus 6P, and the LG V20, but this shouldn't be a shock as Google mentioned in the beginning of last month that select LG phones and Nexus devices would support it. Having said that, Google never actually mentioned specific devices, although many probably already suspected that LG's two latest flagships as well as last year's Nexus phones would be the ones that Google was referencing. There are also some devices that do not work which appear to have been tested along with the others, as 9710 mentions that the HTC Bolt does not work, and it's suggested that none of Samsung's work either at the moment.
While this is unfortunately not a full rollout of the feature support across Sprint's lineup of devices, more devices on the network will end up supporting RCS messaging on Sprint in 2017 as originally noted by Google, so while current phones with support might be a limited list, next year will bring in more compatibility and make it more widespread. There were no more phones mentioned in the post in regards to having been tested with results, but there are some details about how the messaging works and what it allows, such as the ability to send video files that are at least 104MB in file size, according to 9710. If you frequently enjoy sending videos back and forth, this might appeal to you quite a bit.