C.O.
for me? It's as soon as possible. If I miss a phone call - it could be a client telling me about a new position he/she has open or a candidate getting back on an offer.
No, it doesn't matter to me if it's from within my organization, a client or someone else. You treat them the way you want to be treated. So really? I do it as fast as I can without skimping on someone else.
If I am in a meeting and see that I missed a call - I will send a quick text to let them know I am in a meeting and will call when it's over.
If a volunteer situation? Same rules apply. Why would it be different for volunteer? Just because I don't get paid for it - doesn't mean I shouldn't put my best into it.
I take it that someone didn't get back with you - or you got in trouble at work for not responding back in a "professional" amount of time?