I tend to let the answering machine answer the phone, and if I'm talking with someone, I politely excuse myself with 'Oh shoot! I got to stop the dog from whatever! Call you back in a couple minutes!' and then go. It just seems kinda gross.
This thread reminds me of the following episode of This American Life, in which writer David Sedaris contributed this story:
In a men's room at La Guardia airport I watched a man take a cell phone from his jacket pocket, step into an empty stall and proceed to dial. I thought he had come for the relative privacy, but looking through the space beneath the door, I saw that his pants were gathered about his ankles. He was sitting on the toilet.
Most airport calls begin with geography, 'I'm in Kansas City' people say 'I'm in Houston' 'I'm at Kennedy' When asked where he was, the man on the phone said simply 'I'm at the airport, where do you think?'
The sounds of a public toilet are not the sounds you'd generally associate with an airport, and so his 'where do you think?' struck me as unfair. The person he was talking too obviously felt the same way.
'What do mean which airport?' the man said, 'I'm at La Guardia, now put me through to Marty.'
A few hours later I was in Boston, relating the story to my sister Tiffany. 'I mean he actually placed a call while sitting on the toilet!' Tiffany is big on rules, and so I expected a certain degree of outrage. I wanted disgust, but instead she said only 'I don't believe in cell phones.'
'But you do believe in talking on the phone while sitting on the toilet?'
'Well it's not a belief,' she said,'but I mean, sure.' When asked how she explains the noise, Tiffany scrunched up her face and held an imaginary receiver to her mouth. 'I say- Don't mind me, I'm just trying to ...get the lid ...off this jar'
Her face returned to normal and I thought of all the times I had fallen for that line. All the times I had pictured my sister standing helpless in her kitchen. 'Try tapping the lid against the counter top' I said or 'rinse it in hot water, that sometimes works.'
Eventually after much struggle she would let out a breath. 'There we go' she'd say, 'I've got it now.' And then she would say thank and I'd hang up, thinking 'Well it's a good thing she called me.'
You can hear it at http://www.thislife.org/Radio_Episode.aspx?episode=241
and it is about two minutes long, the introduction starts at about 29:20, the story at 29:45. The way he tells the story (all the pauses and emphasis) is hilarious.