I don't know how much data it uses -- I don't have to worry, because I have unlimited data. So using this instead of my "real" phone will save me much hassle when it comes to waiting for phone reps for hours on end. In the past, any interaction with help-desks, or other phone-in places that had long wait-times, could end up using literally all of my available minutes. Now I can call on my Google Phone and sit on hold for free. I only wish there was a way to put it on speaker. But the phone volume is loud enough that it won't be a problem.
Here's the link for the phone app - https://play.google.com/store/apps/details?id=com.google.android.apps.hangoutsdialer.
Thanks to my friend viverra (aka Claire) for encouraging me to try this. For years she's been telling me how useful this would be. I'm glad she patiently kept at it. I'm slow, but I get there eventually.