In the Rezound. there are THREE storage areas to be aware of:
~2GB Internal Storage, this is where most applications and their data are stored by default
~11GB Phone Storage, this is the phones internal "SD Card" some applications can be moved here, some apps will install here if available (depends on app)
16GB SD Card (or whatever size you have), also referred to as external storage or /sdcard/ext_sd - Only for storage of files (music, pictures, videos, documents) or application use. Apps themselves cannot reside here or be executed from here normally (This is largely due to the fact SD Cards must be formatted in FAT32, and FAT tables do not have Linux attributes to set them as system, executable, owner, read-only, etc), although many will save files or install data on this drive if it is available, again, this is app dependent.
The phone has an easy way to list and move supported apps between Internal Storage and Phone Storage, go to Settings-Applications-On Phone Storage, this will give you a list of apps that can be moved to Phone Storage, if they are ticked they exist on Phone Storage, if not then they are in Internal Storage. To move them, just tick the box and this will open the App info screen, then tap "Move to phone storage", depending on app size this can take a few seconds to a few minutes. Not all apps can reside on Phone Storage, for example, any app that has widgets cannot be on Phone Storage, some are written to specifically be in Internal Storage and do not normally support being moved.
There are also apps that can automate this or make some apps that don't normally allow themselves to reside on Phone Storage to be forced there, such as App2SD and there are others too.