Hello and welcome to the forums - thanks for joining!
I too have the ability to have a call waiting (which I can answer, leaving the other person on hold), but I am not sure if it is possible to have 2 calls merged.
EDIT - I happen to be at my parents at the moment and have spoken to my dad (who is a telecoms engineer)... he said that he doesn't think that it is possible from your phone (as a standard phone call)... I believe it could be possible from some sort of conference calling app.