FYI:

• N-Series is compatible with Mail for Exchange. I have lost the count of how many N95's I have installed MfE on.
• You can get N-Gage running on the E71, arguably the most popular E-series phone around. Which comes with a nice SIP VoIP client, VPN, QuickOffice, PDF reader, WLAN, 3G, MfE or Lotus Notes Traveller, among other things, and that is out of the box. Why someone would want N-Gage on an E-series phone is beyond me, though.
• The whole Nokia business is centered around the idea that, regarding devices, one size do not fit all purposes. I know many people that won't buy a phone that doesn't have a physical keyboard, for example.

I don't know other users, but E-Series is fine already in Symbian. Maybe getting a E-Series phone with the form factor of the Palm Pre would be nice, but I assume that would imply S60v5. In any case, Nokia is aiming to unify, but through software, not hardware.