With the upcoming innovations in the world of cell phone technology, a hard but necessary step is closing down of older legacy services. Included in this; is the shutting down of all 3G cellular towers & all their functionalities. This shutdown will impact your phone's ability to dial 911 if you have an older 3G cell phone. So it's important to note what phone you have, if it's an emergency phone in the glovebox.
What popular phones are affected?
iPhone 4 : iPhone 4s : iPhone 5 : iPhone 5c : iPhone 5s : iPhone 5se
Thankfully, cell phone manufacturers have been thinking about the future for awhile & most modern smartphones are more than capable of running on a 4G network. Things do get a bit more tricky however; a phone must be 4G VoLTE capable, not just 4G capable. This means that all models of iPhone below the iPhone 6 will NOT be functional once your corresponding cellular provider sunsets their 3G towers.
Here is a handy link that discusses how you can use the settings inside of your phone to check to see if it's able to be used on a 4G LTE network: Link.
Android phones have been a bit more forward thinking then Apple & most devices made within the past 5 years typically will support 4G. Here is another link that shows what devices should be fully functional once the 3G sunset occurs: Link
AT&T: will have its 3G network sunset in February of 2022
Verizon: 3G sunset for commercial and government fleet customers will come at the end of 2022
Sprint: 3G shutdown is coming in December 2022
T-mobile: has yet to release their 3G sunset dates.