Black Swan is an Google Voice weblication, this means it is not something you can purchase in the iTunes App Store or Cydia. This weblication looks and act like a real iDevice App, but its just a link on your home screen that links to a Safari website.

Black Swan is a feature-rich weblication that enables you to view and manage your Google Voice data just like a native iPhone application. It has been available in beta mode for the last view months and has just been officially launched.

Black Swan has 2 versions to choose from, a free version “with ads” and a Premium Subscription. All you need is an existing Google Voice account and an iPhone or iPod touch running version 3.0 software or higher.

Here are some of Black Swans features:

• Native iPhone look and feel.
• Sync your Google Voice data.
• Automatic and immediate updates.
• Offline access to Google Voice data.¹
• Listen to Google Voice messages and read transcriptions.²
• Swipe to delete calls, voicemails, or SMS conversations.
• Google Contacts import.
• Call using Google Voice or iPhone.

Source [VoiceCentral via tipb]