Ummm....I have to think about this as it was about 1 1/2 years ago. Probably the first thing I heard was my Audi asking if I could hear her. Oh yea, I'm one of those who could understand speech right off. I heard my wife speaking to me and my kids playing quietly between themselves. I remember hearing some kind of announcement over a speaker system. My own voice was ridiciously loud to the point that I had to whisper at first. It didn't sound like my voice either and that threw me off big time (while the others were more or less the way I heard them before). In fact, I had a little tear at that and it was funny that my Audi thought it was tears of joy (believe me I was grateful it worked very well but it was the sheer volume of sound I was hearing that did me in

). I admit it took me about two or three days to really understand my daughter with her higher pitched voice. My son wasn't a problem.
When leaving the center to go to the car, I heard the vehicles and the buses were far too loud. While driving to a restaurant to "celebrate" my hookup, I could really hear the car's engine. My wife was on the cellphone and I heard her side of the conversation pretty well (speaking with my mom and her mom over the hookup). In the restaurant, I was flummoxed by all the clattering of the dishes, plates, people talking, and the music going overhead. I couldn't believe how noisy everything was and I finally understood what I had been missing all these years. I had used the phone to talk with my brother on day three or four. He was amazed at what I could understand and I wasn't missing anything either.
To sum it up, I had a great hookup even though it was so overwhelming at times. It came out even better than I thought it would (I had thought it would take a couple of weeks). I literally was a going concern with speech by day two and maybe a week will all the sounds in general.
Of course, my experience is probably not the most typical one but it shows what is possible given one's background.