Constant names must conform to CS (the entire package name shoudl be used).
I also don't really like Services_JSON but I'm not sure where else this would go..
There should be spaces around all operators (such as = in the constructor and += later in the code).
enc() and dec() should be removed. They don't actually add anything and will only help to confuse things.
There is still "(backslash)(backslash)" in the code. Please use a single quoted string (for consistency).
Docblock class names need to be updated (I see JSON::decode, but it should be Setvices_JSON::decode or whatever name is eventually chosen).
Thanks for taking into account my previous comments.