We have several international trips coming up, and will happily use our iPhone 4s (via Ting's GSM roaming) for voice calls. The phone runs iOS 9.3.5.
We'll be traveling with two other couples, and text messaging between us will be useful. I would like to enable text messaging while not allowing any other data transfer to or from the phone. I can do this by remembering to never launch Safari (or Weather or any other app that requires data) unless I'm connected to a wifi network, but I wonder if this limit can be invoked via iOS settings.