Google maps should work on a regular (non-BIS) data plan. For Facebook, you can use Snaptu or the mobile web version of the site (m.facebook.com).
I think the biggest problem you'll have going with a regular plan is not being able to install apps OTA. Many apps these days don't come in the alx format needed for installing using desktop manager.
When I first got my device a few years ago, I didn't have a data plan at first but with wifi was able to use the native BB browser. I think this will depend on whether or not the wifi service books are pushed to the device. Since you are buying the device from your friend, it might be on it already.
If your heart is set on it, I say try the generic data plan. If it doesn't work, you always have the option to get the BB data plan or do something else.
Posted via BlackBerryForums.com Mobile