[Android Central Question]

For example if someone wants to switch carriers, is it possible to switch frequencies on their phone to match the carrier's frequncies?

[ManiacJoe]

You would think so given the state of technology.
However, even if it is possible, this is not something the user would be able to do.

[hallux]

That depends on the phone actually. If the phone model has support for the radios needed for the new carrier it would be as simple as swapping the SIM card, if the phone is unlocked.

For example - if the phone in hand is, say, the Galaxy S9 (G950U in the US) and you bought it from Verizon all you need to do is satisfy your purchase contract (pay it off so Verizon doesn't blacklist the device for non-payment) then go to another carrier and get their SIM. All the Galaxy S9's in the US appear to be the same, no distinct model numbers based on carrier so they all should have all the US bands or frequencies. Once the new carrier's SIM is installed, it should just work on their network.

That is NOT the case with all phones, but it does apply to the Pixel and Pixel 2 as well as their XL variants, even when bought from Verizon. I also used Verizon as (at this time) all their 4G/LTE phones are unlocked, there is no need to go asking them for an unlock code to use the device with another carrier's SIM. AT&T still locks their phones, preventing use with another carrier's SIM unless you go to them for the magic code...