The company I work for writes business-management software to manage inventory, sales, commission payments, etc. We have been in business for over 30 years and have clients in several countries. Of course, we do provide support for the software, and our support contract specifically defines different types of support calls and specifies how long we have to respond/fix the issue. So when a call comes in we define it based on our contract rules and give it the appropriate priority. This essentially takes care of the triage.

However, we still have some clients who mark every issue as "URGENT" and expect their calls to be handled first... But we are lucky in that our support load is light and we generally have same day turnaround in any case. Having the contract define expectations has been extremely helpful for my role in managing support issues.