it's a reference to a segment on the Accidental Tech Podcast (hosted by Marco, John Siracusa and Casey Liss) where at one point they brought up a guy (sorry I can't recall the name) who has two iPhones: one for day use and another for night use. The idea is separation of private info and work info. IIRC Marco could see some merit to it, but certainly couldn't justify the price for himself.
I bought a Samsung something-or-other Duos so that I could have a business number and my private number route to the same phone. It takes two SIM cards.
OK that is cool. I would have gone with Google Voice or some other proxy, but dual SIMs is awesome. Can you manage do-not-disturb and ringtones/notifications per SIM?
http://atp.fm/