Cellphones are small, mobile wireless devices that allow users to make calls and have additional functions beyond traditional landlines. They require a subscription to a service provider. Modern cellphones are much smaller and lighter than early "brick" models, and have color displays. While cellphones have become necessary, overuse may negatively impact memory, brain cells, and direct human interaction due to radiation exposure and addiction. Potential negative effects include health issues, environmental damage, distraction, and cost. Further research is still needed on health impacts of long-term cellphone radiation exposure.