I call all over the country in my postion and deal with different accents and dialects daily. If I call California, no accent unless they moved there from another area. Most of the West Coast, same thing. The Midwest has different accents, as does the south. The East Coast, too has several different accents. Boston & Staten Island, New York are the two that come to mind. If I call Staten Island or Brooklyn I sometimes have to get an Italian interpreter. Ditto the interpreter (Spanish) for certain areas of California, Texas, or Florida.
I spent 4 years in Kentucky during college. I like to joke that it took me 4 years to learn the proper pronunciation of the word Louisville (Lou-ah-vull). However, now it takes me no time to get a southern accent back, although I have lived in Chicago again almost thirty years. I have even caught myself doing it during a call to a Southern state. The best was the call where a guy called me & I could tell that he was from Louisville just by his accent!
There are many accents in the US- all part of the individual cultures that we grew up in. An example of this are my Indian friends who actually speak better English than I do because they were taught British English, not the American version.