But tbh, customers aggrieved at your working practices are simply not worth having. If they don't trust you enough to do the work, they probably won't trust the output of it either, which all that it entails (not paying etc).
I've been a consultant in a previous life, and the best customers were invariably the ones who just let you get on with the job.
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.
But tbh, customers aggrieved at your working practices are simply not worth having. If they don't trust you enough to do the work, they probably won't trust the output of it either, which all that it entails (not paying etc).
I've been a consultant in a previous life, and the best customers were invariably the ones who just let you get on with the job.