JAL: java application loader used to load the application on to j2me devices.
JAM: java application Manager manages installation and de-installation of java application on the phone.
When you specify the url of jad the JAL first loads the jad and jar files on to the phone.
Then you have to install the application this was done by JAM or JAID(java application Installer and De-installer for i85).
Comming to your question JAM verifies the content of jad and jar files (size of jar specified in jad must match the size of the jar, etc), and then it will install the application on to the phone.
And I think JAL also uses the content of jad.
After installation when you launch the application JAM call the startApp() and destroyApp() methods.