What I did for my number 6 on my Strawberry Shortcake cake was to roll a long sausage of gumpaste and then taper the ends. Curl the ends under (in other words, "style" your number) and then gently push a skewer or two into the number where they won't be seen. Then let it dry and you can stick it into the cake.
I follow the same procedure as AnnieCahill, but I use a 50/50 mixture of fondant/gumpaste.
Yep mine is fondant with tylose kneaded in.