I know this is true, because "Mama" was his first word.
The other night, Fabian was changing Roman's diaper (Isn't he a good dad?!), and asked me to get some pjs out for Roman. I walked into the closet and Roman turned his head to look for me, and uttered the most precious words a mother will ever hear, "MA MA." I stuck my head out of the closet and questioned, "What?," even though I knew exactly what he had just said. Fabian reassured me, by saying "Yep, and he was looking for you!" I preceded to ask Fabian if he was jealous. He told me, no; and I jokingly proclaimed that he should be, because Roman had just said "Mama!" (I know, I'm terrible!)
He has since called me Mama several times!
Roman has also been saying something very similar to "hey!" So, I might be getting a "Hey, Mama" sometime soon!