Typically you'd just raise your prices to factor in support costs. You'd have different margins for each industry.
Realistically, the reason you're unable to raise your prices is because you're stuck competing with companies that simply don't offer customer service themselves, and hence would undercut you.
If there was an appropriate amount of public outrage (and ideally legal repercussions) toward businesses not offering sufficient customer support, then your competitors would also have to increase their prices. You'd be no worse off, and general customer satisfaction would improve across the board.