okies, well first things first.
your correct in that the two classes depend on one another, and
you should fix Traffic.java before attempting to work on subscribe. Now, i havn't worked with J2ME before, so my help somewhat becomes limited. Searching for the 'java.lang.SecurityException: Application not authorized to access the restricted API' error in google i saw that a suggestion to achieve success is to change the restrictions, allowing Traffic to access Subscribe.
sorry my knowledge doesn't go deep enough to help you with this, some possible area's of interest:
http://forum.java.sun.com/thread.jsp?forum=196&thread=468046&tstart=0&trange=15 (i think that one will help you remove your error)
https://coderanch.com/forums/f-41/JME (that is
java ranch's j2me site.. )
hopefully you get it all working! just give the permissions a go yourself from your initial link, and i suggest looking at javaranch's j2me as your problem is more specific to that topic..
best of luck
-twans
(by the way, it is common practice to define your class with a capital letter, ie public class Subscribe.. not subscribe )
=)