Here's a quick rundown of what will not work without a Blackberry data plan.

1.Blackberry Messenger will not work.
2.No OTA downloading as the Blackberry Browser is part of BIS service books and will not be available to you, however Opera Mini will work fine for browsing.
3.MMS on blackberry is part of service books also so you will not have picture message capabilities unless your provider has a workaround for it.
4.No genuine push email (via the native email client).

With that being said, any applications you install on the device will have to be installed via Desktop manager (.Alx & .cod files) and Java apps (.jad/.jar files) can be placed into a folder on your BB media card and then installed from there. That is of course unless you find a friend with BIS via your provider and do as described in the above edited post. There are many Blackberry Applications that will work without BB data and many that won't so you may have to do a trial & error to find the setup that works for you.

Happy Berrying!