In PhoneGap 3.4.0 you can call:
cordova build android --release
If you have set up the 'ant.properties' file in 'platforms/android' directory like the following:
key.store=/Path/to/KeyStore/myapp-release-key.keystore
key.alias=myapp
Then you will be prompted for your keystore password and the output file (myapp-release.apk) ends up in the 'platforms/android/ant-build' directory already signed and aligned and ready to deploy.