Apples Messages app got some big upgrades in iOS 18, but one with the biggest potential impactRCS supporthas had a slow rollout among some carriers. Fortunately in iOS 18.4, Messages is bringing the feature to a lot of new users, including those on Google Fi, Mint Mobile, and more.RCS expansion hits Messages for new carriers in iOS 18.4RCS is the best way for iPhone and Android users to message each other.Unlike the longtime SMS standard, RCS enables a variety of great iMessage-like featureseven in your green bubble threads.RCS features include:typing indicatorsread receiptsmuch improved media sharingand tapback reactionsBut carriers have to enable RCS support before iPhone users can use it.Until now, the three major US carriersAT&T, T-Mobile, and Verizonhave all supported RCS. Customers of lots of small to midsize carriers, however, have been left waiting.iOS 18.4 shrinks that list significantly by enabling RCS for T-Mobile MVNOs. These include:Boost MobileGoogle FiMetro by T-MobileMint MobileTello MobileUltra MobileUS Mobileand moreApple has yet to update its carrier support page with the new RCS additions, but it was confirmed throughout the iOS 18.4 beta process.To check that your iPhones using RCS, go to Settings Apps Messages RCS Messaging. Then in conversations with Android users who have RCS enabled, youll see RCS in the blank message box at the bottom of the screen.Did your carrier add RCS in iOS 18.4 or a prior update, or are you still waiting? Let us know in the comments.Best iPhone accessoriesAdd 9to5Mac to your Google News feed. FTC: We use income earning auto affiliate links. More.Youre reading 9to5Mac experts who break news about Apple and its surrounding ecosystem, day after day. Be sure to check out our homepage for all the latest news, and follow 9to5Mac on Twitter, Facebook, and LinkedIn to stay in the loop. Dont know where to start? Check out our exclusive stories, reviews, how-tos, and subscribe to our YouTube channel