GroupMe, a service which enables the creation of chat groups via data connection (or SMS as a backup), has bumped all mobile apps available on multiple platforms to version 4, except Windows Phone. According to an email sent out today, the app on Microsoft's platform will be updated soon.
Currently on version 3.5, GroupMe was last updated back in August where a number of improvements were made, including a cleaner UI and much desired functionality. GroupMe is now owned by Skype (Microsoft) so we expect to see better platform support in the future.
You can download the current version from the Windows Phone Store for free. Until version 4 is available for Windows Phone (possibly only 8 being supported), one can check out what's new on Android and i OS.