Beagleboards with 512mb of RAM and 600mhz CPUs are powerful enough to be Desktop PCs: they're also small enough to be portable. With modular pre-certified cellphone components from Telit such as the GE862, the opencellphone project proved in 2006 that it is possible to create your own mobile phone. The HBP/D aims to build on the prior success of that project and the success of the Hy Research MID project, to create a powerful and open smartphone project.
The Telit UC-864-G is the most likely candidate as the radio module, thanks to it supporting Quad-band GSM, Tri-band 3G/HSDPA, and having A-GPS all in the same compact space.
The fact that Telit's documentation is publicly available without requiring an NDA, including full application notes, full hardware and full software disclosure, including the "Digital Voice" Codec AT command-set, makes Telit's excellent products an easy choice.
Learning the lessons from HTC smartphone and iPaq PDA reverse-engineering, the Trolltech Greenphone, the OpenMoko, the myPhone, the opencellphone and from a proprietary ARM+GPS+GPRS product, the HBP/D will be an open project from the ground up.
The initial focus will be to get incoming and outgoing phone calls up-and-running as soon as practical, so that software developers can engage with the project at a very early stage.