I was discussing creating a rough draft of the Service level Agreements and how to get all the departments in your organization on board. It will take time and work to get all the appropriate departments to agree that this is the right approach. Show them "what's in it for me". That's the best way to get cross functional consensus on your service level agreements. No customer service/call center or IT help desk software can do this work for you. Cultivate you allies in the organization. Explain the benefits of having Service Level Agreements from their perspective. Before sitting down with them, ask yourself, "how can Service level Agreements make these other departments succeed?" When you know the answer, run it by a few people to "reality test" it. Will these departments understand and believe the benefits?
If you have measured the actual case resolution times based on approximate severity levels and you have created a straw man SLA including this data, then you are ready to get the rest of your organization involved.
1. Meet with individual managers to explain how their department did on your test of priorities and response time.
2. Explain how the SLA goals will impact how they are already doing.
3. Use your existing allies within other service groups to prepare the way for broad acceptance.
Here is a great White Paper on Implementing Service Level Agreements. See https://www.givainc.com/wp/it-help-desk-software-cloud-whitepapers.cfm