The Pocket Townstone is a limited functionality Townstone. It can only be placed in a pocket dimension, and does not expand the size of the pocket dimension. However, it only costs 500g. The Pocket Townstone can be upgraded to a normal townstone for 10 plat. The Pocket Townstone's sprite is identical to the normal Townstone's sprite. However, it is purple. the command to upgrade a pocket stone to a normal townstone is /townupgrade previously confused to be /townexpand                       
Screenshot (109)

The sprite of the Pocket Townstone in the Shop Menu