The ultimate time waster: solitaire. Every phone should have it, and this version is the straight-up, old-timey, standard Klondike flavor that everybody knows and loves. The same company makes a pretty decent Hearts app, too, if you’re looking for something a bit different.
Link: Klondike Solitaire
Similar Apps: Hearts Deluxe, Solitaire, Spades!
More on Time.com: 50 Windows Phone 7 Apps to Get You Started