The "Download Now" link directs you to the iTunes App Store, where you must continue the download process. You must have iTunes installed in order to open the link, and you must have an active iTunes account to download the application. This download may not be available in some countries.
From Finarea SA:
Voipdiscount is a mobile application that lets you make (free) voip calls direct from your iPhone. You can start saving on your Mobile Phone costs by simply installing the Voipdiscount application. Select any contact from your contact list which is accessible in the app and start your call using Voipdiscount anywhere, anytime. Voipdiscount operates over multiple internet connection options (3G, WiFi, GPRS, Edge, UMTS) directly from one integrated friends list. FEATURES - Make Voip phone calls on your iPhone - Connect to Internet using Wifi, GPRS, or UMTS - Latest internet technology at lower rates and perfect sound quality - Select regular contacts from contact list to make a call - Works all around the globe: anywhere, anytime - Bypass voip blockades with Voipdiscount - Detailed call information