Docs to Go is not BES dependent. Starting with OS 4.5, the standard edition will be included with the option to purchase the premium edition. The difference between the two is that the standard only allows saving, viewing and editing of documents; while the premium allows that plus creation.

HTML email will also be included starting with OS 4.5. The caveat is that it also needs to be enabled server side as well. What this means is that until your provider activates HTML email on their BIS, or your company on their BES, you won't benefit.