Smartphone carriers account differently for data transfer, texting (SMS) and phone calls. A carrier's cellular data plan is based on the number of bytes transferred each month over the cell towers for Web pages, email, questions and answers (Siri, Google Now, etc.) as well as apps that access the Internet either in the background or while people use them. If the phone is connected to a free Wi-Fi hotspot, there is no charge for data, but as soon as users travel out of the hotspot, the cellular data service takes over.
Phone calls and texting may be unlimited, or plans may have a limit of call minutes and text messages per month with additional charges if exceeded. However, although data transfer over cell towers may be unlimited as well, customer data plans usually charge by the number of gigabytes of data per month. Data is often sharable by all family members on the plan.
Video Can Exhaust the Data Limit
Unless you are in rural areas with limited coverage or in urban areas with heavy congestion, cellular service is always available, and you can watch videos via your cellular data plan. Phones default to using a local Wi-Fi hotspot if available and Wi-Fi is turned on in the device. However, videos consume many megabytes of data, and the meter is running when the cellular data is being used.
In 2015, T-Mobile introduced Binge On, which offers subscribers unlimited streaming of standard-resolution video (480p) from selected content providers, including Netflix, Hulu, ESPN, HBO and Showtime. See cellular generations
and Wi-Fi hotspot
A Data Transfer Warning
This app for Samsung's security camera cautions the user that continuous monitoring via cellular will use a lot of data.