A few days ago I had to phone a company headquartered in Nebraska to arrange the return of a piece of equipment. I was immediately struck by the accent of the woman who took my call. She was almost certainly a native speaker, and her vowels were mostly unremarkable for a NA accent. Except her accent was non-rhotic. "Part number" was [ˈpɑːt ˈnʌmbə] and, most surpsingly, her pronunciation for the letter 'r' in isolation (when spelling) was [ɒː]. Does anyone recognize this as a feature of any NA accent?
Is this a feature in Nebraska?
Hmm. She was probably from somewhere else. Take a look at the map on "Wikipedia: American English". You'll notice that Nebraska is not part of the small non-rhotic areas. So, she could have 1) been from one of those non-rhotic areas, or she could have 2) had a speech impediment or 2) was speaking African-American vernacular English. Did she sound like she had a speech impediment (it would probably affect all r's) or did she sound like a speaker of African-American English? If not, then she was probably from Boston or New York, or somewhere else back East.