If you want real time email, don't go with the voyager. As far as I know, you can only sync to one email account and it only offers verizon's basic calender that you get on any normal cell phone. It won't sync with google calender, outlook, or any other desktop app.
As for the iphone, my wife's company uses them as a corporate phone and she absolutely despises it. She has said that as far as a multimedia phone goes, it's fantastic. However, when it comes to business oriented work, it's not that great. No real keypad makes it difficult to reply to emails. When we're together and she gets emails, she'll actually forward them to my phone to reply. Also, AT&T's edge network is a lot slower than verizon's EVDO so the download speeds are pretty slow when she's not in a hot spot.
I don't really know that much about blackberries since I've never used one. All the people I know who have one absolutely love them though (they aren't called crack-berries for nothing).
I was faced with the same decision a couple of months ago when upgrading from a treo 700P. I ended up deciding on the xv6800 over the I760 mainly b/c the XV has a better camera and is a little smaller (fits in my pocket pretty well). They both have the same size screen and run windows mobile 6 professional which should have no problem syncing w/ your Vista.
Other phones you might want to check out are the Sprint Mogul and the AT&T Tilt if you're considering leaving verizon.
I'm very tempted to buy an Ipod Touch for use as a PDA and stick w/ my current regular cell phone but I'm now leaning towards getting a smart phone. I don't know anyone currently using a smart phone so I haven't had a chance to get an idea for the 'feel' of one but I do know exactly what I want to get out of one.
Here are the features I want and any input you may have is very appreciated!
-Web browsing: WiFi is good but I live in an area where it's spotty at best so some broad band is probably called for.
-Verizon Wireless: For the simple fact that I still have a year left on my contract and my employer offers a discount. "IF" a phone is out there that is absolutely perfect I would consider paying the early termination fees.
-E-Mail: Need to be able to check in real time.
-PIM: I live and die by my electronic PDA calendar. I use Google calendar alot but also need to be able to keep an off-line record. Also I would like to have a contact manager program that allows seperate fields for first and last names (small point but very irksome when you don't have it)
- Syncing: Must be able to sync PIM w/ desktop (Windows Vista 32bit Premium edition)
-Screen size: Bigger is better
These are the main features I'm looking for. Here are some that I'm looking at:
Samsung I760 - seems very nice and offered by VZW.
Blackberry - good industry standard, offered by VZW but I've never seen the OS or User Interface.
LG Voyager - not a smart phone but cheaper, nice interface but unsure of PIM and Web browsing.
Iphone - if, *IF* it really is all that good may be worth paying VZW early termination fee. (would have to be spectacular)