Depending on the version of SugarCRM you're using, we have mobile apps that connect to your SugarCRM instance, allowing you to create, retrieve, update, and delete records.
Just a point of clarification, we do not have a plugin for the Mobile version. The information Dan provided pertains to the Sugar Mobile application, which does not directly interact in any way with the iOS Mail app (or any other iOS mail app).
There are no current plans for a Mac OS version of the plugin. It currently does not exist due to technical differences between Windows and Mac OS that in turn do not facilitate the ability to port it.