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.
Group SMS adds a "Reply All" feature to SMS, enabling a group of users to communicate using a single thread. The use of the feature is free and it uses the built in SMS capabilities and plan of the iPhone. The Group SMS can also be used by users that do not have a smart phone.