Complex sentence: The first phase, between "Plaza Once" and "Caseros" was planed to be opened by the end of 2003, but current estimates place the opening in late 2006 or 2007.
Split into simpler sentences: The first phase, between "Plaza Once" and "Caseros" was planed to be opened by the end of 2003. Current estimates place the opening in late 2006 or 2007.