Small numbers of Gauls served as early as Krimisos (341BC). During the second war with Rome, as many as 9000 foot and 5000 cavalry might have served at one time with Hannibal alone. In DBM, Gauls in the early armies are classed as Wb(S) and in the later as Wb(F).
The gallic foot supply both Early and Later Carthaginian players with both anti-foot capacity and command and control problems, all rolled into one package. They are also pretty vulnerable to mounted (arguably not the Wb(S) if 4 deep). The cavalry in the later list are pretty cheap, though not terribly effective, graded as Cv(O).
Gallic Wb(F) in Carthaginian service. I use different color schemes to make them look as different 'tribes' - I run a third each of the different color schemes (yellow, red, orange), (blue, grey, green), (brown, black, red).