I had a Gameboy Color and GBA (SP) before, but I bought them years after launch when they had a good library. "Gaming on the go" wasn't that important to me.
The PSP was the first mobile device which hyped me so much that I had to have it at launch. And I got it even way before the European launch date by importing it from Canada (for a very good price).
There were a lot of awesome games in its first year that I loved: Ridge Racer, Wipeout, Lumines, Twisted Metal, Tiger Woods and Hot Shots right from the start (yeah, I was into golf games that time) and Burnout Legends, SOKOM and GTA: Liberty City Stories later that year.
There weren't many DS titles in 2005 I was interested in and I had some issues with the first hardware model, so I waited for the DS Lite which fixed most of these issues.