Both of those handsets are crippled in various ways by the carrier (ATT). It may really it boils down to taste. A lot of folks have already commented that buying the unlocked E71 may be a smarter move. If they can eventually cook up a custom ROM for the Jack perhaps that might give it an edge over time. You would really benefit from doing some intense reading in the various Symbian & WM forums to get a better sense of what's out there. There are plenty of apps for both WM & Symbian. You have to ask yourself *which* of the available apps you really need. Howardforums is a nice place to get down to earth answers too.
I am trying to decide between the new Jack or the E71x. The E71x fits everything except I know nothing about the os. Can I get apps for this as easily as win mobile? Been down this road before where made wrong choice.