Here is an example of something I made a few years ago: http://games.clarklavery.com/meshMorpher/index.html
Move your cursor left/right over the page in order to make it work.
The 3d artist started with the same sphere for each model, and by only moving the vertices around, produced the four models. Then you load up the models and use linear interpolation for each vertex of the mesh to position in somewhere in between the first and second model. The example does a bit more complex math than just linear interpolation by adding some random offsets, but should work for any obj models with the same vertex/face counts.