The Wizard power
Foe to Frog (Heroes of the Fey Wild) allows the wizard to change the target into a tiny beast.
My question is: can the polymorphed target retain its spell casting ability if it has the appropriate limbs for somatic movements and a mouth for vocal ability?
An example: a necromancer turned into a frog. Ribbit ribbit (magic missile!). Interestingly enough, I don't consider a frog a beast, yet that is the example given.