Register Hardware notes that Apple has modified the iPhone SDK to specifically allow developers to include sweepstakes and lottery functionality in their App Store applications.
The new rule is unambiguous:
"3.3.17 Your Application may include promotional sweepstake or contest functionality provided that You are the sole sponsor of the promotion and that You and Your Application comply with any applicable laws"
The report notes that developers must clearly state in any contest rules that Apple is not a sponsor of nor responsible for conducting the promotions.
Also referenced in the report is The KaChing Button, an application introduced in December that previously only served to allow users to make a novelty "ka-ching" sound. The $0.99 application was updated last week, however, to include sweepstakes functionality under the new SDK terms, allowing the application's developers to offer "up to $1000" per day in prizes over the next month to random winners selected from those pressing the KaChing Button within the application. Daily prizes thus far have been at the minimum $100 level and will presumably be increased should revenue from application purchases support such payouts.