What are you trying to do when you connect it? You can't transfer files between the devices - you can only use the bluetooth to allow the iPhone 3G or higher to serve as a hotspot, or for peer-to-peer connectivity (multiplayer games, etc). Check out these support links:
Bluetooth will allow the use of keyboards, headsets and I think speakers with the iPad. Here are the supported Bluetooth profiles.
You can't transfer files via Bluetooth from your phone to the iPad if that's what you want to do.