i have found its quite possible to run most low rpm pager motors off an arduino pin and coin cell. it all depends on current draw. a quick test will show nearly all types will run directly off the coin cell or even low current button cell. maybe not full speed.
i have even managed getting 'nano' scale model airplanes to fly direct connect without transistors. the trick was to use multiple pins, in some cases all 8 portb. the real problem is preventing mcu reset but even that is solved with proper bypass and noise suppression. generally using a transistor is more practical with fet being better choice than bjt with its lower on resistance and no need for base resistor.