24x7 support and how to charge?

The best way is to create an app or a website that connects to paypal which automatically allows customer to call or create ticket as well as charge the customer based on timings. For example if the customer open your website or app during day it would be X dollars and if they visit it at 2.00AM then X+Y Dollars. I would not advise subscription model if they do not frequently call you.

I'd be happy to help you with this. I've run a lot of services businesses with SLAs and different contract/hourly values based on levels of service.

"Riskbased" pricing is not far from what you suggest, so you are on the right track: Calculate call frequency and how much each call will cost you (time, resources). Divide it over your working time, and add a profit margin: Then you have a monthly fee for 24x7 support.

If you want, you could monitor individual frequency - maybe somebody uses your support more than others and would freeride on a fixed rate? Then you could price based on number of uses of your hotline pr. month, or software version (if some versions crash more than others).

This is how you do it in insurance, where "usage" is random, and each use (claim) will cost you money. If you want to know more about this, feel free to sit up a call, or send me a mail.

Best regards
Kenneth Wolstrup