We have two Revolutions with the same problem. Neither will open any attachment that comes in email. The exact error wording you get is "attachment is too big to download." This happens on pictures, pdf, word, excel files, nothing will open.
This problem started happening straight out of the box. Neither phone had a ton of apps loaded (as I know sometimes some apps don't play nicely together), We did try countless apps that claim to help with this but the reality is they only either help with your gmail attachments or they only help send attachments (not receive). Even after trying them, the phones still won't sent attachments.
Also the other issue is that I found was the skype feature will not do video chat. Both of these phones are intended for business use so attachments and video chat were two features that would be most useful.