Pop up for more minutes

I’ve been told I can buy more minutes when I run out, but I’ve looked and I’ve looked and I can’t find anyway to do it. Nor can I find my billing history to determine when my minutes regenerate. My suggestion is when we run out of minutes, have a popup appear that asks if you would like to buy more minutes? That’s what a lot of programs do. You can then indicate how many minutes you want to buy. I don’t know if this is something you can do or not.