Indeed, there are two new Phone features. One is called Remind Me Later that is a quick way to skip a call but be reminded to call back. You can be reminded in an amount of time, or when you leave your current location (or when you arrive somewhere, like Home or the Office).
You can also use Facetime now over 3G, which will open the floodgates for Apple's video service. You should keep an eye on data usage though if you plan to use Facetime on 3G on a regular basis.
Anything new for Mail?
The mail app has the new VIP inbox feature from Mac OS X Mountain Lion that only displays emails from people you've highlighted (by favouriting in Mail or Contacts). It's a great way to view emails from just the people you're interested in.
What's this Passbook I've heard of?
Passbook is a completely new app from Apple that displays vouchers and receipts from companies that have designed apps to work with Passbook. A typically example is that you book a air ticket with a supporting company (say British Airways) and your ticket is sent directly to Passbook on your iPhone. Because it's location-aware it'll serve up tickets when you arrive at the airport, and the barcode displayed on the screen of the iPhone is your ticket to board the plane. It sounds great, but will depend on support from companies. It's all part of Apple's long term plan to integrate the iPhone with businesses and the retail environment.
Anything I probably haven't heard of?
You might not have heard about WiFi plus Cellular, a new option that enables apps to switch seamlessly from WiFi to a Cellular connection. If you're loading a web page, for example, in a WiFi zone and move out mid-load, it'll carry on with the mobile network. It seems an obvious feature but one that will make a big difference to how seamless the operation is.
Some features from Mac OS X 10.8 Mountain Lion like iCloud Tabs and Offline Reading list will be brought over to iOS 6
It also takes privacy much more seriously with a system Apple is calling "data isolation privacy".