I have started this with MJ, i have done a bit of reading in EC and it is what Mum did with me and i was out of nappies day and night by 12mths.
I asked her about this the other day as i was wondering about how i communicated it to her and what about wiping etc.
She started sitting me on a potty after each feed for a few minutes. If nothing was done that was fine, if i wee'd or pooed well there was a bit of clapping. but the time i was 12mths i would hold on til the morning and do a big wee then and during the day i would communicate somehow (mum cant rememebr) or i would go and get the potty and bring it to Mum so she would know. This i cant call toilet timing, i knew what i needed to do and when and worked out how to communicate this to my mum.
I do how ever agree that a 3 mth old cannot make the decision when and when not to poo, but obviously the mum and baby take cues from each other and know whats happening.
lets face it, 3mth olds are starting to learn things, MJ knew the sound of me undoing my bra, a friends baby knew when he had a bib put on at this age that he was going to get a feed and would start to get impatient, so its not too much of a stretch to think that this baby is leaning that the potty is where to poo.

The chinese do this and there are other cultures that do too.
As i said i have started molly jane sitting on the potty, there is no pressure, its convinent for us and possibly we will learn from each other.