The quest for a truly open smartphone: can it be done?

The recent release of the Symbian kernel source code under the Eclipse Public License (EPL) has generated some discussion in the open source software community about the challenges of building a truly open smartphone platform. Software freedom advocates are concerned because none of the existing open source mobile platforms with mainstream viability are entirely open. Smartphones are playing an increasingly important role in our daily computing activities, a trend that's only going to grow as the technology becomes more pervasive. If smartphone devices can't be opened up, then those computing activities will forever be restricted by network operators, handset makers, and platform vendors. The implications are clear, but the real questions are: to what extent is it necessary to open up a phone and to what extent is it possible?