EWS is Exchange Web Services and since at least 5 years supported by Linux, iOS, OSX, Symbian, and every single other operating system and product vendor worldwide. It\’s a standard by Microsoft. Only Problem is, Microsoft themselves don\’t support it. Microsoft makes it thus virtually impossible to use windows phone on a professional or business level. As it\’s needed to organize contacts into groups / sub-folders. It\’s very weird, that Microsoft doesn\’t support EWS and thus officially states it doesn\’t want business and professional customers where Apple and other companies are saying: yes, sure we support this feature which is a must have for professional and business customers. Why would we refuse professional and business customers? They bring good money into the basket! But MS keeps repeating: no, customers who pay damn good we don\’t want! We will not support anything for the professional and business community. We don\’t want their money. Go away! I wonder why MS does that?
I think you\’re asking the wrong question here. I think the more correct question is "When will Exchange ActiveSync support Outlook Groups". I would ask that question in a more relevant community. Try here for starters https://community.office365.com/en-us/f/158