I'm in love with email-based support as I am on both sides of the chain. When I raise a problem, the engineers on the other side can work at their pace, escalate when needed, and I almost always get a reasonably good reply. I can dig deeper if I wish, and I'm pretty sure the guys on the other end are doing their best.

It works the same way when I'm helping someone else: most reasonable people don't expect that if they make an audio call I will magically solve their problem faster. Maybe it will be slower and they will get a lower-quality ad-hoc solution.