Calls on is a term that can be used to describe a variety of activities. Visits (6 letters) is when someone physically goes to a place or person. Asks (4 letters) is when someone requests information or assistance from another person. SEES (4 letters) is when someone looks at something or someone. USES (4 letters) is when someone takes advantage of something or someone. Taps (4 letters) is when someone lightly strikes something or someone. USER (4 letters) is when someone takes advantage of a service or product. All of these activities can be described as calls on.