The problem is, there is no "move to sd" option when you try to switch over an app. This is a problem because the internal storage is 1 GB and phone storage is about 200MB. This is not enough to install more than a few apps depending on what they are. In the app manager, there is a button for "move to phone" or "move to internal storage." But there is no move to sd. Plus the phone won't read apps off of the sd card anyways. Last, there is no option for choosing default storage area and even if there was there is still the above mentioned problem that the phone would not read the sd card apps.
I would look into apps such as App2sd in the play store. I think they create a symlink in internal storage that is linked to the actual app data on the sdcard.
I used this on my old phone. It worked pretty well.