Instructions
Look at the dial and find where the finger stop is on the dial plate. An authentic crank telephone has a finger stop at approximately 3:00.
Examine the side of the dial, which should be silver in tone. If the side of the dial is black, it is probably a reproduction and not an authentic antique.
Look for modern touches, such as Phillips-head screws, which did not exist in the early 1900s. If you see these details, the phone is likely a fake.
Examine the finger wheel. Authentic antique phones had a finger wheel that bent down at the edges.
Look at the metal tag at the bottom of the phone. It should say "American Tel &Tel CO" or "WESTERN ELECTRIC CO". The tag should be held on the phone with two rivets, one on each side, and in general should be difficult to read due to the age of the item. If the tag is easy to read, appears to be peeling off, or in general looks cheap or new, the item is probably a replica phone.
Unscrew the bottom plate and examine the inside. If there is a zinc plated stem screw and it looks like the brass is new, the phone is not an authentic antique.