We knew that DataViz was going to demo their Documents To Go product at MWC for the Apple iPhone and Dieter Bohn had a chance to sit down with them and get a live demo of the product in action on an iPhone. At this time Word document editing is working with Excel editing still not quite there yet. Their product will provide Word and Excel support along with PDF viewing. They also do have cut and paste support within the application.
With Apple's development limits, there is no way for DataViz to provide native email client attachment support, but there may be some way to use a desktop client to get documents onto your iPhone and store files locally.
The DataViz Documents To Go application should be available in the 2nd quarter of this year.