The webOS address book displays all the information available for each person from multiple different sources. A single person's entry could have, for instance, phone numbers from an Exchange Server, a street address from Google, and a picture from Facebook. All of this would be displayed to the user together, without regard to where it came from.
The calendar works the same way. The webOS can pull calendar information from a variety of sources and display it all together, with entries color-coded by their source (
as shown here). If all this data at once is overwhelming, the user can choose to display or hide the entries from individual sources. When there's a event happening from a calendar source that's currently being hidden, its time slot is, though empty, a slightly different shade, so the user knows there's something happening then.
If someone has an Exchange email account and a Gmail account, the webOS can display messages from both on a single list.
Naturally, replies go back through the appropriate account, and the accounts can be displayed separately if the user prefers, but the concept is to simply the situation by letting the smartphone deal with where messages are coming from, and let the user just read their email.