The "could not activate cellular data network" error means your iPhone won't be able to use the mobile data you're paying for ...

Unlimited data plans are expensive, and smartphone applications can run up the tab if you're not careful. Keep on eye on these apps for efficient data usage.

When you're always on Wi-Fi, it's easy to overlook just how much data apps like Spotify use per month. But this becomes an issue when you have limited cellular data. Maybe you only have a 5GB monthly ...