I feel like every two years I need to call my carrier and complain if I want a decent deal. They will do things like upgrade my plan on their website to have 10 extra gigabytes of data but won't upgrade me to it until I contact them. There's also all the new member exclusive deals that I feel make it impractical to just sit on one plan for an extended period of time.
Whenever I change employer and they get used to my habits. My employers have paid my phone bill since 2012, so they pick whatever is cheapest for them.
Fun fact: Largest bill (so far) was ~4000 USD equivalent for one month
I was over in TX for work, and we had a production system there that was needed online ASAP. So I grabbed a 4G router to allow the VPNs to connect and used one of my spare SIMs (associatedwith my cell phone plan). In 99% of the cases this would not have been an issue, as it's mostly telemetry and the occasional SSH session. Until a geophysicist noticed that it was online and spent the next few weeks pulling down terrabytes of raw seismic data for testing.