I recall my high school days where we were doing the same but with dumb phones, with a screen that would just show one or two lines of text. (crackberry.com)
Old dumb phones could run for a week or more on a charge, but modern smartphones often struggle to make it through an entire day. (howtogeek.com)
Phone locking applies to nearly any type of cell phone, from the lowest, cheapest dumb phone to the highest end smartphone. (howtogeek.com)