Can I use tethering to share my iPhone's connection with my iPad?
iOS 4.3, available for free download on March 11, 2011, includes the Personal Hotspot feature introduced with the Verizon iPhone 4. You can get Internet access via 3G on the iPhone, then use your iPad via a WiFi connection to the phone to share the phone's Internet connection. It doesn't use Bluetooth, but it effectively works as well (better, in fact, since Personal Hotspot supports multiple connected devices and WiFi is faster than Bluetooth).

Here is a story from Macworld that discusses how the Personal Hotspot feature works. It's pitched to the feature on the Verizon iPhone, but it should apply to the GSM iPhone 4's running iOS 4.3 as well.