Static linking is an bad idea. It's not clear at all if LGPL license legally allows static linking whitout releasing the application source code. ... So if application developer wants to develop closed source Qt application then static linking against Qt is an bad idea, unless application developer wants to buy a commercial license for Qt.
LGPL says that application user must always be able to re-link the application against the same or another version of the LGPL'd library. This is not any problem if application is dynamically linked. If application is statically linked against LGPL'd code then application developer must provide application source code or atleast linker objects so that user can do the re-linking. If some special tools for the process are needed then developer must provide those too. The only official source for iPhone software is AppStore. If you have iPhone which is not jailbreaked then you can install apps only from the AppStore. If I'm correct then some kind of digital signing is used to make sure that no unofficial applications can be used.