When I am out of the office/home and away from a internet connection, (wifi), I would try to make a call, use Maps or try to use another app, the error message would tell me that it can not make a call or use the particular app until the iPhone is connected to the internet.
This has never happened before and it is very inconvenient. How do I fix this?!
The problem is the cellular data got turned off. With it turned off the device will only use those apps with an internet/wifi connection. To resolve, open the iPhone Settings. Tap Cellular and then make sure Cellular Data is ticked on, (green). Additionally, scroll down the list of apps and make sure they are ticked on for using cellular data. One note of caution: if your phone plan has limited data ticking on any app will use some of the data included in your plan and may cause you to run over the allotted monthly amount.
Once complete, back out and try to use the apps again.