But I'd like to know how to do this. Twilio already provides me with a mechanism to cheaply receive and process calls, but how do I charge the users for this? anybody ever look into this? Google doesn't turn up much that is useful.
Also, you don't want to charge for Installation problems, and God knows they are the source of many support calls (I'm looking at you, InstallShield).
Customer Support can be a benefit to the company that makes the software, because they signal bugs or imperfections that you want to address. For every customer that calls, there will be many that don't bother and don't buy either.
Try two-tiered support: a free Support Forum with 24-hr response, where customers have the option of searching for questions from others who had the same problem, and what the solution was.
Phone support is available to premium customers who buy a yearly maintenance contract.
lets say I want to run a sex hotline. how do I charge you for calling?
(I'm not actually running one, but thats the example)