Be careful! My calf started cramping once about a year ago during a step routine. I ignored it since it wasn't too terrible, and finished the workout. The next time I did step, I felt a pop, and my calf muscle tore. Only within the last month has it finally, totally healed - after PT, seeing docs and even having an MRI.
So if your calves are cramping, they're trying to tell you something. Back off. Stretch. Stretch a LOT. Re-evaluate your workouts, and maybe take it back a notch to give the muscles a rest. Better yet, take a few days of complete rest.
I assure you that if I ever experience this again with any muscle, that's exactly what I would do.