Many Americans will lose cellphone service today when AT&T becomes the first major provider to switch off its 3G communications network. This will make 3G devices incapable of handling calls, texts, or accessing the internet without Wi-Fi available. THIS INCLUDES CALLING 911!

It is unknown how many users will be affected. The switch may also affect an unknown number of systems ranging from home security to medical devices to fire protection services.

T-Mobile will be switching off its 3G in July, and Verizon plans to switch December 31st.

The Federal Communications Commission advises visiting your wireless carrier to determine whether your phone is affected. AT&T, Verizon and T-Mobile have details on which devices are impacted. For example: Apple iPhones older than the iPhone 6 will lose function. Some devices may only require a software update to continue working once 3G is retired.

For other devices, check with the manufacturer to determine whether it requires a software update or an upgrade.