I was about a 2b before the Coppola treatment. Now, I am a 2a - or maybe even a 1c (not sure). You can see some pictures of what my hair looks like now straight. The fotki website is in my siggy. I lost all of my frizz and pretty much most of my curl. It is pretty straight now. I had it done 3 weeks ago. Also, I had this done last summer, too, and it wasn't as straight as it is now. Maybe because it was more humid last August than it is now....not sure.
Before I had it done, I just talked to the stylist about it a little, and she told me about the process. It is pretty easy. I really like it for the summer months because the humidity is horrible on my hair. Now I can just either air-dry it or blow it dry in about 5 minutes. I don't have a huge amount of hair.
Since you're a 3b, you will probably lose a lot of frizz and some curl - maybe you will just be wavy. Your hairstylist will probably have some better advice for you.
I am just enjoying having straight hair for now because I know that it will wear off in about 2 months. Also, it is very, very soft and shiny now and feels much healthier. No split ends!!