Users have reported that emails are taking an excessive amount of time to download from SBS to their iPhone Exchange accounts. I've witnessed this as well. Recently, the fetch time (to retrieve 0 new emails) jumped from less than 5 seconds to over 30 seconds (consistently). This one has a few moving parts so we would need to review configurations and logs for SBS server, Mail Relay and iPhones to investigate possible causes so that we can develop the appropriate action plan.
We have also recently migrated many of our business processes to a web based ERP/CRM application built with Python. We will need to configure email gateways for this application to get it to play nicely with our on-premise SBS.