When time stops it stops in a reference frame. There is no motion in that reference frame but the frame can still move through spacetime relative to other reference frames. Think of light as a permanently frozen object. It pops into existence and does not change. It can still move through spacetime. The concept of instantaneousness does not apply to frozen objects. They don't experience time ever.

Similar to motion, a reference frame where time stopped can spin. That's how the singularity in a black hole behaves. Time is stopped in it but it still spins. When matter falls into the black hole angular moment adds up so it can spin up or spin down while still experiencing no time (remaining frozen).

Note that light frequency is not a movement in addition to the movement of light along geodesic lines. A frozen object can have internal frequency, spin, and momentum.

Cell phones still use 800 MHz. When they transitioned from no encryption analog AMPS to encrypted digital D-APMS in 90s they made it possible to gradually transition to D-AMPS. And all subsequent technologies were designed to support gradual transition. They run 4G and 5G in the 800 MHz band these days.

In networking, using data means using bandwidth (a fraction of the total network speed). It is similar to renting rooms in an apartment building. When you rent a room you are using space in the building. Since the life time of the building is finite using space in the building costs money. Similarly when you watch a video you are using a fraction of the total network bandwidth. The higher the resolution of the video the higher the fraction of the total network bandwidth is used. The longer you watch the higher the fraction when averaged over a month. And similar to a building network equipment life time is finite so using a fraction of the total bandwidth costs a similar fraction of the total network cost.

They use a texting service provider such as Bandwidth. Bandwidth is basically a mobile carrier without towers and other cellular networking hardware. But they connect to other carriers exactly the same way a real mobile carrier does.