Here's what Foursquare itself says about the latest version of Swarm for Windows Phone:

"Wanna see what we've been cooking up? In this release, we've stepped up our sticker game. For starters, all your stickers now have a new home in their very own tab. It's a quick way to check on your progress and see hints for unlocking stickers, which will be super useful since we've added a ton of new ones. See how many you can unlock. And stay tuned for even more fun things coming your way soon."

"Also in this release, we have introduced messages! We've added the ability to message your nearby friends to quickly and easily meet up."