BJT can amplify both voltage and current, it depends where you take the output (from BJT). NPN common emitter amplifies voltage, Common collector (emitter follower) amplifies current.
Here is a good reading of BJT **broken link removed**
The thing is that BJT is driven with current (you have to get some current to base to make transistor to open), but FET transitors need voltage to open (there is no current in FET gate). So all the equation with BJT are based on the base current. But this does NOT mean that they can only amplify current.