At one point in my life before I joined VeriSign, my wife and I both operated consultancies out of our house. We often picked up each other's phone lines if it was more convenient, feeling free to fend off the telemarketers and pass along the calls that mattered.
One day my phone rings. I'm in the kitchen getting a drink, so she picks it up. As I walk back into our joint office, she's holding the handset and looking at me.
"It's about your company AmEx card," she tells me, puzzled look on her face. Puzzled for the simple reason that my one-man consulting firm did not have an American Express card.