Sure about that? That was one of my major reasons for looking at a Pre.
I know I could have multiple calendars from a single source, (I have always had 2 Mobile Me calendars - a work and personal one), however I am 99.9% sure you couldn't have calendars from multiple sources, (eg Exchange and Mobile Me).
Either way, the fact I can now see both has made me a happy bunny!
- D
EDIT: You could be right TechFreak85. Found a
Wikipedia article which says this from OS 2.0:
Calendar
Multiple calendars supported in Calendar with color coding (desktop colors only preserved if using Mobile Me)
New "Calendar" menu in "Settings"
Push calendar
However, I'm not sure of this includes calendars from multiple sources. I was 99.9% sure that previously when I enabled my Exchange calendar on my iPhone it said it would stop my Mobile Me calendar being sync'd (or something like that!).
Anyway, like I said, a happy bunny here in Oxfordshire!!