My first flight as a regional FO was on the B1900, pre-dawn departure. Thankfully the first leg was a maintenance repo flight so no pax and it was my leg. The plane was frozen we had to warm it up, we were doing the first flight of the day checks, I was trying to keep up. When we were ready for takeoff and the CA asked me tell them were're ready and when I actually called them with the company callsign that's when I knew I was with the big boys now. Being used to 6 to 8K for cruising in the 172/seminole. It was a trip watching the altimeter go from 0 to 10K and above in what seemed like a few minutes. The most challenging part for me was interacting with the pax, since the 1900 doesn't have an FA, and trying not to make it seem like it was my first day. I never really had any problems flying or managing company ops. Training is tough but it's really fun once you make it out on the line.