from the main article:
Portability of the estate tax exemption means that if one spouse dies and does not make full use of his or her $5,000,000 (in 2011, or $5,120,000 in 2012 and $5,250,000 in 2013) federal estate tax exemption, then the surviving spouse can make an election to pick up the unused exemption and add it to the surviving spouse’s own exemption.
What a great concept, right? Well, keep in mind that historically the “AB Trust” system was designed to do what the portability election does.
My impression is that portability does what the AB Trust does w/o having the trust..............provided you do the right thing...............which is to file an estate tax return for the 1st to pass even if no estate tax is due.