Do you have any kind of ticketing system? A template that leads them through the what / when / who / where questions you normally have to follow up with could be helpful.
If not, try to find a couple 'champions' at each location and get them to be your technical point of contact there if possible. These are normally people that are at least a little tech savvy and understand that you don't take your car to the mechanic and only tell them "It makes a 'whomp whomp whomp' sound"
It can take awhile. There's a certain type of person that likes to just throw problems over the wall. If you can explain that a little more information will help you both and get it resolved a little faster, they're usually on board with that. If not, you can always give them a log to fill out for you - day/time, device, and what they were trying to do. Tell them once they have 5 or 6 entries in the log to send it to you.