I have developed an application with Flex Builder 3 and it works fine.
When I compile the same application with Flex SDK compiler mxmlc,
the application compiles fine and it works partically except the HttpService
request gives me a Security Sandbox violation.
I am compiling with -use-network=true
What else do I need to do with Flex SDK to get out of this sandbox? It works
fine with Flex Builder 3.

Probably FB, being an IDE, allows you to act as if you were on the network, so
-use-network=true may be ignored (unless you execute the SWF outside of FB).

The command line probably respects -use-network=true so for testing set to
false, and when putting the SWF on the network set to true.