Good airline pilots are good for many reasons. One is that they keep their passengers updated when things might not appear to be going as originally planned. Like when you're in the line-up to take off at some airports and the captain comes on the P.A. and lets you know that your plane is sixth in line to take off. That's helpful information! It didn't fix anything, but just getting the status update helps you feel more comfortable.
That's how we, as IT professionals, need to approach tech support. When there's a lull in the action, before they can start to feel like maybe they're being ignored, let them know the status of things! Letting them know, for instance, that you're waiting to hear from the manufacturer on something helps them know you're doing all you can on their behalf.
Put yourself in their shoes. If you'd start to feel impatient or neglected at a certain point, become their advocate and proactively give them a status update! It takes very little effort and goes a long way towards earning their trust and appreciation.