Karen Walker

so ive been licensed for about 4 months now and i mostly do 2m FM on the local repeater but im starting to get into HF a little bit and i notice some people use phonetics like every single transmission and others barely ever use them. im a little confused about when youre actually supposed to use them. like is there a rule or is it just a feel thing i know the NATO ones, Alpha Bravo Charlie etc, but sometimes i hear people using completely different words and i wasnt sure if thats allowed or if theyre just making stuff up. one guy on 40m said something like America Boston Chicago for his call and i didnt know if that was an older system or what. just trying to figure out when i should be using them and whether i need to stick to the NATO list strictly