There are currently four Galileo satellites - however the good old USA has said that in the event of a conflict or global conflict or some such thing which requires them to turn their own GPS system off they will 'disable' the European system. From colleagues at work I understand 'disable' in this context means 'disable permanently'.
There are no navigation devices currently available that use the Galileo system only.
Personal comment: if the EU Member States had left the whole mission to ESA it would be up and running by now. However it was taken over by the European Commission - hence it is years late and only four satellites are in orbit from the 12-15 needed.