This is not exactly a howto since there are already many howtos/tutorials available and exact instructions are always device specific. But since it is a interesting topic here a short summary of my experiences of liberating an old Samsung Galaxy S GT-I9000.
Reasons why you could want to do this:
Reasons why you could not want to do this:
Components I used:
A more complete list of possible software options is available at the Free Software Foundation Europe.
A few notes on the apps: