My grandfather, who is a Russian from the Smolensk region has an interesting manner of speaking.
One of the peculiarities is his use of the -ом/-ем suffix for masculine nouns and proper nouns in instrumental case that initially would have -ой or -ей when speaking about doing something with someone. I.e. "с Юрком" (vs "с Юркой"), "с Сашем", "с Жорком", "с папом" (с папой), etc.
Could this be an alternative form that's in use in some region, or that came over from another language, such as Ukrainian? Or is it an obsolete archaic form? Or is it just his own invention?