Loading an object from PHP session, does it call constructor?

Answer 1

The constructor is only called once: when the object is created (with the new keyword, in your case new GeoIP()).

Answer 2

The answer is no, as the object is not being reconstructed. What is called however are the magic __sleep() and __wakeup() methods, the first when you store it to $_SESSION and the second when you retrieve it.

You should take a quick look at this thread to make sure you've considered some of the problems of using $_SESSION to store objects.