Here's a sampling of what we encounter or anticipate encountering...
iPhone w/iOS v4+
iPad w/iOS v4+
Windows Phone 7
Droid w/OS 2+
Providing exact models is difficult because it depends upon what is purchased by the end user. Additionally, the majority of our encrypted email recipients are individuals outside the organization. Our MEG encrypted email piece has been in place since June of 2010 and to-date we have not received any complaints from our mobile user base about not being able to read encrypted emails on handhelds... Pat yourself on the back.
Thanks so much for your reply. Exactly the kind of data I was looking for. Matches up to what I was thinking the major handheld platform are.