Contacts on Windows Phone is handled via the People app, which links up to various online accounts -including Windows Live, Google, Facebook, Twitter, Outlook, and LinkedIn - and pulls together contact info along with tweets and status updates. It also displays images of friends pulled from social networks on the outside tile.
Expectedly, this can create a long list of contacts for folks you might not need at a moment's notice (especially online pals), but People lets you sort the master list to leave out contacts from certain sources.
Adding multiple social networks may well result in multiple profiles coming over for a single person. But, you can link them together easily by clicking the chain icon at the bottom of a contact page, and finding the other contacts to combine as one.
As noted above, the People app also includes quick access to updates from social networks like Twitter and Facebook, as well as a centralized list of your own recent updates across networks, though heavy users will want to use the dedicated free Twitter and Facebook apps (from the marketplace) to keep up with friends' updates.
The dialer uses an elegantly simplistic interface with large digits that cumulatively take up more than half of the screen, and typed-in numbers can be saved locally from here as well.
The Phone app also displays a history listing when opened, and allows quick access to the People app for looking up contacts.