Instead of booking a 30 minute meeting, that only has maybe 10-15 minutes of work talk and 5-10 of personal talk, we might instant message for 15-20 mins spread across a whole day.
Or if things get complicated in the first few minutes we'll just have an adhoc call for 5 mins, then IM whatever details we thought of after hanging up. That 5 minute call is similar to swinging by someone's desk.
Some people still insist on booking the 30 minute meeting, and that can make sense when you have several people or some "meetings are my job" people are involved (upper management, marketing, sales, etc).
It seems like about the same amount of work talk either way, but usually less personal talk. Introverts love that, extroverts are missing out.
It also varies by person. Some people are too vague in their typed messages so it's better to talk on the phone. Other people have really thick accents and English may be a second language, so a detailed IM conversation can actually be more efficient than talking on the phone for both parties.