Use the present form in if or time clauses that refer to the future.
You can use will, may, or might in predictions. Will is more certain than may or might.
You can use be going to when there's evidence now for a future event.
Everyone's going to use cards more in the future. We're (not) going to be using cash 20 years from now.
Every cell phone will (probably) have a chip. Cash (probably) won't be disappearing soon. There may not be a need for cash. We might be using phones.
If we only use cards, what are kids going to do? You'll use your cell phone when you buy things in the future.
