How can I use my iPad with a Bluetooth headset or hands-free?
See iPad: Using Bluetooth headsets and keyboards in Apple’s Knowledge Base:


  Bluetooth car kit functionality is limited to audio output. Additional car kit features are not supported on iPad.


The article on supported Bluetooth profiles on iOS might also be of interest. As you can see, the first-generation iPad doesn’t support the Hands-Free Profile (HFP 1.5), but the iPad 2 and the third-generation iPad do, although the Phone Book Access Profile (PBAP) still isn’t supported.

There’s also this thread on the support forums where a lot of people can’t seem to get a bluetooth headset working with their iPad. As user Dave Lucente says:


  The iPad is not a phone, so it should not be a surprise that cell phone head sets will not work with it.