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 Andreas Amann:
The application e-fon vPBX connects your iPhone to the virtual PBX of e-fon. As of now your mobile calls display your companys fix net number and are charged at the lower VoIP rate. The comfort level is identical with regular mobile calls. For example you can access all contact lists stored in your mobile device.The phone calls are handled via the standard GSM network and can be initiated at all locations with GSM coverage. There is no need for WLAN access. The quality of the conversation is the same as with regular mobile calls.The application can be used only in conjunction with the vPBX service of e-fon.For additional information please turn to our website at www.e-fon.ch