Congrats on getting an iPhone 4. Looks like a really impressive phone!

The inability to accept calendar items within mail is a complaint with my iPhone as well. I never found an app to correct this- but never looked either. Always thought is was poor of Apple to not set it up to allow acceptance of meeting notices this way.

As to reminders, if you manually set it to alert you 15 mins before, it turns on the automatic reminders and also will then bold the date so it'll show up.

The way I use my iPhone calander for work/business, is I forward meeting invites and such to my home e-mail account. Accept them in outlook there, and then when I sync my iPhone, they'll show up in my calander there. Not the most elegant, but it works.

Apps:
Weather Channel (free)
Facebook
1Password (love it)
Ballistic (for me at least )
Stanza
pic2shop
Remote
Showtimes
Drinks Free
MotionX GPSLite
Ebay
Kindle
iChess
Sol Free
SoundHound
Labyrinth LE
iHandy Level
Dictionary
WhitePages
Units


Let me know how AT&T works out for you. In my area, I'm actually going to have to retire my iPhone and switch to another option - they're just no good here.