While the official launch of Rematch is later this week, on the 19th of June, if you bought the Elite or Pro editions of the game, you're able to log in now and get some hours in passing, shooting, and defending so you've got a bit of practise before the proper launch.
However, if you and a friend don't have the game on the same platform, you won't be able to team up with them at launch. But, as explained in a post on X/Twitter, developer Sloclap is planning the feature to be included post-launch.
<social>https://x.com/PlayRematch/status/1934529603244028143</social>
It's described as one of the "top priorities" for Rematch going forward, meaning we shouldn't be waiting too long before we can all play together. Things like crossplay can help keep a player base healthy in the weeks following the launch of a live-service/multiplayer title, so we'll have to see how long we'll be waiting before being able to play with our buds no matter the platform.
Rematch launches on the 19th of June for Xbox Series X/S, PS5, and PC.