There is this prestige class called Elemental Savant, which makes the character, actually, an elemental (with all the immunities AND the ability to be raised from dead, not to mention one can even be Bone Elemental, or even Plasma Elemetal. Not omega awesome, but at some points, it's a really interesting and badass choice). The spellcaster becomes of an outsider type and at the 10th level becomes a real elemental, which even changes his appearance (even trough just a little bit). But, the description of the class still leaves something unexplained Can the 10th-level Elemental Savant acquire the traits of his elemental type at will? For example, an Air, or Electricity one-can he levitate just because and get trough fences like they're not there at all? Because, basically, for a living gust of wind it would be really easy... Or are the adepts of this class just gain minor appearance changes and elemental traits and the atacks?
Elemental Savant is from Complete Arcane. Their tenth level capstone power Elemental Perfection reads:
This means at tenth level you get these traits - nothing more. Note you don't "acquire these traits at will," they are always in effect. So yes, if you are an Air elemental shaman you can fly 100 ft., perfect. The description in the second paragraph seems pretty clear that you're not now 100% made of that element or anything - though even if you are it doesn't matter, see below.
The class also says if you're going outside the standard elements, the GM will need to figure out some of what that will mean. If an Electricity Elemental can pass through metal, then you can - if that's not a defined power (meaning something explicitly listed speed and movement modes, natural attacks, special attacks, and special qualities) they have, then not. Note that by the rules an air elemental can't pass through a chain link fence even though "they're air," it's not one of their RAW powers. Your GM may vary that based on their vision of how the world works. But you are not entitled to anything as e.g. an air elemental savant other than fly, whirlwind, air mastery, darkvision, and elemental traits (most notably: Immunity to poison, sleep effects, paralysis, and stunning, Not subject to critical hits or flanking, Elementals do not eat, sleep, or breathe.) That doesn't say gaseous form, that doesn't say immune to physical attacks, it doesn't say anything else.