How can I make my objects/classes more portable?

[SemenOV]

From my basic understanding in Object Oriented coding, PHP in my case, you want to make all your classes pretty much independent of one another. I have just started my object oriented application so it is a great time for me to make changes in it's early stages.Here is my situation where I break this rule or whatever you want to call it. I have a sessions class that has a set method which lets me set variables to a php session and I have a view method which let's me view the value of a value that has already been set using the set method. So far it probably sounds OK but then on every page of my site I need to access session data or the session objects I should say. But then besides every page using the session objects, I also use them in all my classes that need the session value. I believe this is where I have messed up, because now all these other classes rely on the session class. Any ideas on if this is wrong and if it is, what are some ways I can avoid it but still have access to the session data in the other classes and still have my classes be portable plug-n-play into other future applications?