I've found that most really successful people return calls much faster than moderately successful people. So the question is: are they successful because they return calls OR do they return calls because they are successful.
I'm not sure.
But I think it is wise not to chance it. Best bet to return calls and email quickly.
A lot of inbound emails are for people who are trying to sell you stuff or for things you don’t want. With those emails, my rule is that if the email is written well, takes my interests into account, and is polite and short (without big attachments), I'll email them back and at least say that I'm not interested. That way their time can be respected and they don’t have to follow-up with me.
All people should follow this rule.
But more importantly, emails from colleagues, friends, or business acquaintances should be replied to ASAP. If you are on a call with someone and you agree to get something to them by Wed, then you should definitely get something to them on Wed. And if you slip, you should let them know. And if you don’t let them know, you should at least respond to their emails asking you about why you haven't responded. It is only courtesy.
I personally take notes on everyone I interact with on the following items:
– do they get back to me in a timely manner?
– are they on time to meetings?
For people that respect my time, I give them a star. If that person is ever in need of anything in the future, I go out of my way to help them. If the person does not respect my time, they get a minus sign. I’ll be less likely to respond to help requests from those people in the future.
Being nice to those around you, especially those that are a few rungs down on the ladder, is an essential to being a good citizen. And of the people you are dealing with, you never know who might be someone that can yield influence over you in the future … so respect their time now.