Depends on what a "call" represents. A 15 minute chat, happens once every other week or so? Just do it, don't count them. A 2-hour meeting? If it's part of prospecting for new business, you do it and eat the cost; if it's the readout for a project you've delivered, then you accounted for that cost in your SOW. If it's ongoing support, and they're not a house account you bend over backwards to keep happy, book a billable day or set them up on some kind of use-it-or-lose-it bucket of retainer hours.