You may want to right-click and choose “Save As” to properly download the file, it should always have the “.ipsw” file extension. The CDMA model means a device does not require a SIM card to use the cellular antenna, and is typically Verizon and Sprint in the USA.
The GSM model indicates the device requires a SIM card to use the cellular antenna service, in the USA this includes AT&T and T-Mobile.
GEEKSN0W IPHONE 4S IOS 7.0.3 UPDATE
Users who prefer to update iOS manually using firmware can use the direct IPSW links below to download the files from Apple’s servers:
Users who choose this method will need the latest version of iTunes installed. Users can also download and update to iOS 7.0.3 through iTunes by connecting their iPhone, iPad, or iPod touch to a Mac or PC and choosing to Update. The OTA update weighs in between 70MB and 120MB depending on the device being installed on.
Apple has released iOS 7.0.3 for iPhone, iPad, and IPod touch users.