Just to contribute to the confusion, many Black Americans also use "ain'." As far as I can tell, an ain'ie is a grand aunt or an aunt who cared for nieces and nephews and/or who pass down family traditions. When my niece was born, I made sure that I was not "auntie" but ain' J because I have a lot to pass down!! I was born and raised in California, but my family is from East Texas, Arkansas, and Louisiana. Because it is a title of honor, I do not view it as slang. Ain' is simply an offshoot of the beautiful, colorful foilage that is SAEE!
For the record, I pronounce aunt phonetically.