They have already announced this. Go to the Apple page and watch all the introductions for the phone and under technology-->OSX you will see it says you can e-mail, surf, and talk all at the same time.Speculation contains the usual suspects:
Info on the remaing apps. Camera, notes, calendar.
Details of what kind of data plans are available / required.
What I would love to see, is that somehow they were able to allow the internet and phone to be used at the same time. (Without wifi)
Otherwise, if you're surfing the web on the train/bus to work, you can't use your phone.
Watch the page I mentioned above. Just because current phones can't doesn't mean the iPhone can't. Normal phones don't do visual voicemail either after all.I know you can't use GPRS/EDGE while on the phone, but you should be able to use Wifi. I don't see why you couldn't, unless the software itself prohibited its use during a call.