Android OS introduced Bluetooth as an open API in version 2.0, but early versions like the well known Donut (1.6) and, one of the most famous in Motorola devices, Cupcake (1.5) included Bluetooth support in the OS for hands free communications, files exchange and communication with PCss (and Macs).
Of all projects around the web that enable Bluetooth in pre-2.0 devices, I liked android-bluetooth (http://code.google.com/p/android-bluetooth/) very much. Basically because it was design for compatibility with 2.x releases of Android. This was archived by keeping an API as similar as the official one but changing the package name of the classes (Android does not allow 3rd parties classes inside android package).

It is very important to check if the Android devices allows Bluetooth comms, either because the module is not present or because it is not available. For doing so, just use this piece of code:

If everything goes right, you have to register for broadcast messages like “discovering devices”, “discovering finished”, “did finish connection with device” and so on. That is very easy to do in Android

and then, it is necessary to implement the Broadcast interface

Some other configurations are needed by this framework, including a configuration file and registering receivers and activities in the Android Manifest. For a complete working example check out my BTExample project.
BTExample