Every app needs to be signed. Even for JB iPhone. But in this case you can sign in by your own certificate. Here is a guide how can you make your own certificate. Name it "iPhone developer".
Then, in Xcode, you need to make "New Run Script Buildphase". You can do it in Project -> New Buildphase -> New Run Script Buildphase. Then write there this piece of code:
if [ "${PLATFORM_NAME}" == "iphoneos" ]; then
platform=/Developer/Platforms/iPhoneOS.platform
allocate=${platform}/Developer/usr/bin/codesign_allocate
export CODESIGN_ALLOCATE=${allocate}
codesign -fs "iPhone developer" ${BUILT_PRODUCTS_DIR}/${WRAPPER_NAME}
fi
Then finally you have to add one line into Info.plist. In that file make a new line and put in there as a Key: "SignerIdentity", as a Value: "Apple iPhone OS Application Signing".
That's it. Plug in your iPhone and get ready for testing!