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, e-mail, 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 are measured by total minutes per month, and texting is measured by the number of messages per month. While phone calls and text messages may or may not be unlimited, the data transfer is generally based on a fee for a maximum number of bytes, which may be as little as 10 megabytes per month to as much as 18 shared gigabytes for a family plan. Video Can Exhaust the Data Limit Unless you are in rural areas with limited coverage or in urban areas experiencing heavy congestion, 3G/4G cellular service is always available, and you can watch videos via your cellular data plan. Phones default to using the local hotspot, but many models can be configured to switch back to cellular data if the local hotspot is too weak to provide a continuous signal for comfortable video streaming. However, videos consume many megabytes of data, and the meter is always running when the cellular data plan 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, Wi-Fi and Wi-Fi hotspot.