"Mommy" is the first word they say in our imaginations. My son said "Daddy," "cookie" and "McDonalds" before he got around to learning "Mommy."
Also, my niece called all men "Daddy" until she was about 2 1/2 and still occasionally calls all women "Mommy", and she's almost three now. My almost-five-yr-old occasionally slips and calls me "Daddy," and that's been consistant since he started talking.
My oldest was late on everything. He sat up at 13 months. He crawled around 16 months and walked at almost 20 (just before his little brother was born). He didn't talk clearly for YEARS (in fact, looking back, we can't really remember at what point we understood him clearly). Turned out, he couldn't hear. He'd had multiple ear infections, and the crappy pediatrician we took him to (we didn't know he was a crappy pediatrician!!) never once suggested he get a formal hearing exam, just kept giving him antibiotics. By his second birthday, he'd made up his own language, and two months later, he had tubes put in his ears, and began improving immediately. Still, he's six years old now and only just beginning to speak in a way that is clear to all the adults around him. Another fun little perk: he taught his little brother and his cousins HIS language.
Oh, and you cannot be assured that he can hear and understand perfectly at that age, because they can't tell you. The way the pedi ENT put it, it was like he was just under the surface of the water in a swimming pool. He could hear and understand well enough to respond, he just couldn't hear the individual sound definitions and details well enough to reproduce them correctly. We would talk, and he'd know what we were talking about.
Other than that one issue, what we learned is that you cannot compare kids. Just because one does something one way, that does not mean others should be expected to follow suit. And of course, that goes both ways, because "all kids" do it this way, that doesn't mean it's how one particular kid will do it, and that doesn't mean something's wrong with the one. With my 20-mo-old walker, he didnt' get up and take a few steps, toddle and fall over. He got up one day and ran across the house in the same way all those babies that started walking six months earlier did. Now that he's six, we realize, that's just how he does things. Neither of my boys do anything the "normal" way, and the best advice I was ever given was to never buy a Parenting magazine, never buy a book on baby development or anything. I used to, and they scared the heck out of me!
Encourage, but try not to compare, worry, or pressure. Keep his appointments, get his hearing checked properly, but don't just assume something's wrong because other kids do it another way.
The person who suggested ECI is correct, they do housecalls, and you can call them up until the age your child is three years old. At the third birthday, the child is switched over into the public school system, which is a little more difficult to navigate, but ECI does help prepare you for that transition. Generally, it's just speech therapy, and of my son's kindergarten class, about six kids do speech therapy. It's considered part of the "special education" department, but is literally nothing to feel bad about.