Microsoft tracks specific issues with mobile devices that use ActiveSync.
See Current issues with Microsoft Exchange ActiveSync and third-party devices. (Article ID: 2563324.)
Why all Exchange ActiveSync experiences are not the same… and how to know what you are getting
Apple.com: iPhone Support Enterprise page
Apple.com: Apple Enterprise Support for Exchange ActiveSync and iOS
Apple Enterprise support is available via an Enterprise Support Agreement, as per the above link, or via a Cross Platform and Command Line Interface PPI (pay per incident).