I am living in an area where line voltage is 220V. If I have access to all 3 phases, is it possible to create a "socket" with output voltage of ~110V, without use of a transformer? This is primarily a thought experiment, rather than a project with definite scope.
Triac based light dimmers do this.
Varying the firing angle of the gate results in a reduced RMS output voltage. The output from this can be rectified and filtered however extreme caution should be exercised because the circuit has no galvanic isolation from the Neutral/Active lines and cannot be earth referenced if ELCB's are intalled.
You don't say where you are. I'm not an electrician, but in the US, any one of the three phases will be 120 V to neutral, so the easiest way to get 120 will be to attach your outlet from one of the three phases to neutral. You don't need any electronics of any kind, but to be safe, you need to install everything per the electric code with circuit breakers and so-on. In the US, neutral wires are usually white. The three phases are red, black and blue (red and blue may be marked with tape). Ground wires are bare copper or green. Ground should not deliberately be used to carry current. It is for fault currents only.
Have you checked all legs against neutral? Some 3 phase transformers tap so that two legs are 110v. http://en.wikipedia.org/wiki/High-leg_delta