The rep you talked to is full of ****.

Wi-Fi does NOT require any sort of data plan, nor do you need one for syncing your phone with your computer. You'll only need the data plan if you plan to use any Internet-enabled applications (IE, chat programs, etc.) without hopping on a Wi-Fi network. In that case you'd be using Verizon's EVDO network and that's when the data plan comes in.

That being said, the unlimited data plan is a really nice thing to have. Although Wi-Fi networks are plentiful, it's very handy to be able to hop on the Internet from anywhere and not care about locating a network, entering a key, etc. Since data plans are treated as a feature rather than part of your contract, you can add, drop, or change them at any time. Unfortunately, the Verizon pricing is a complete ripoff compared to Sprint's.

One last thing - if you don't want any data plan at all, it is best to disable EVDO connectivity on your phone so you don't incur any per-KB charges. I forget the rate that Verizon charges, but it's something pretty exorbitant.

Hope that helps.