AT&T shut down its 3G network today.
It is the first U.S. carrier to do so and more carriers will follow suit this year.
T-Mobile plans to end its 3G services at the end of March and Verizon will do so by the end of 2022.
The move is an effort to transition to more reliable and efficient networks, including 4G and 5G.
Certain devices will no longer work after Tuesday, including 3G Kindles, 3G flip phones, the iPhone 5 and older Android phones.
That means those devices won’t even be able to reach 911.
Some home alarm systems and medical devices will also be affected.
Certain car technology will need to be updated, including some roadside assistance systems like Onstar.
Some users will be able to get around the lack of 3G by using WiFi, but it will depend on the device.
In some cases, users will only need a software update.
AT&T said fewer than 1% of mobile data traffic uses 3G.