An unnamed Microsoft representative told Trusted Reviews on March 9 that there's a "Microsoft Edition" of the Galaxy S9 available in the US. Trusted Reviews said the Microsoft Edition phones come with "Cortana, Excel, Skype, OneNote, PowerPoint, Word and Microsoft Launcher, plastered atop Android 8.0 Oreo, out of the box."
There's no mention of a Microsoft Edition of the Galaxy S9 on Microsoft's Store page. I asked Microsoft to confirm such an edition exists and have heard nothing back so far.
Update (March 12): A Microsoft spokesperson confirmed Microsoft is selling the Galaxy S9 and that its store employees can customize these phones with Microsoft apps if customers want, but did not confirm that there's anything called a "Microsoft Edition" of the Galaxy S9. The official statement:
"The Samsung Galaxy S9 available at Microsoft Store is the same phone you can purchase elsewhere. Microsoft applications including Office, OneDrive, Cortana and Outlook do not come preinstalled, but when you purchase from a Microsoft Store, our experts can personalize the device with Microsoft's productivity applications so every customer is able to work, play and connect on their device when they leave."