I am assuming, though I don't think I am far off, that there are many people that definitely use phone minutes. The more tech savvy we get as consumers, the better we can use the options available to us.
Here are some thoughts:
A buddy of mine that moved to KY for work got a job working for IBM as a contractor doing hardware upgrades for State Farm in the local area. Mainly, he installs printers (the bane of any IT professionals existence). Because he is a contractor for IBM, he gets no Admin privileges. If the install goes smooth, no big deal. With printers, it never goes smooth. He spends a lot of time on the phone with tech support.
In the tower industry, installers spend hours on the phone with turf vendors, manufacturer's support, carrier NOC support etc. These guys will literally wait on hold for hours. I have seen two phones side by side on hold with different companies for 3+ hours.
And last but not least, I work with a guy who went signed up for a new AT&T account when he bought his Nexus 5. He already had a Google Voice number, and has been using it for some years. He bought a HUGE data plan with the least amount of minutes and SMS as possible. He uses his data connection for phone services, SMS/MMS etc. It works for him. His WiFi at home is great, so his calls sound great. The moment that WiFi signal gets poor, his call quality gets poor. When his AT&T signal is down to 1 bar, either on LTE or HSPA (4G), he can still get a call through sounding pretty good.
So yes, there is still a huge demand for voice minutes. The biggest issue with VoIP (Skype, Google Voice) is that the data connection required to do so has to be reliable and consistent. Ping times need to be stable in order for the call quality to be consistent. VoLTE is a different beast all together and will likely work very well assuming the carrier networks offering the service have their network setup properly.