I have the data turned off on my phone but would like to turn on the data for the use of one app(a credit card reader for my small business). Is this possible? I don't want to end up with lots of data charges
Since you have an iphone go to settings>cellular> scroll to the bottom, there will be a list of apps where you can either disable them from using data or enable them to have data access. Disable all of them except the one app you mention. Then turn data on and only that app will have data access.