I only train my calves once a week...but I mostly only train them for injury prevention purposes.
I used to do them 2x per week. Sunday would be standing and Wednesday would be seated. I did like the Nelson Montana ideas of 75 reps total...however many sets that took, with LITTLE rest.
I hit standing on DE/rep lower day and seated on ME Lower day, so twice a week. I only train forearms directly once per week, but they get hit a lot on other days just from holding heavy weights (no straps).
I would like to start hitting my forearms twice a week I think. I recently heard from a guy that had huge forearms that his grew a lot after hitting them up to three times a week instead of once. What do you guys do? Wrist curls and wrist roller?