I haven't seen a phone do real instant startup from being powered off in a very long time. The different OS on these things have become more and more bloated and have longer and longer initialization times.

In normal use, most phones spend the majority of their time in a sleep mode and they do wake up from that nearly instantly -- a second or two. Likewise, the edge has varying degrees of power saving -- turning off the LCD, and going into a full sleep mode when the two halves are closed. The edge wakes up from the full sleep state in about 2 seconds.