This is my employer's support model, and it works pretty well - all customers get unlimited ticket/email support, and you can upgrade to phone and live chat sup

This is my employer's support model, and it works pretty well - all customers get unlimited ticket/email support, and you can upgrade to phone and live chat support for a percentage of your monthly bill. It's like the saying that 20% of your customers use 80% of your support. This way you can incentivize those customers to pay a premium for even more of the support package they obviously want. Everyone else can have the minimal support interaction they prefer.