Yogurt is usually churned into buttermilk: lassi, as it's called, is excellent, especially if you make the yogurt (dahi, or variations on that: in Bengali it's doi) at home: you take some milk, put a small amount of the yogurt you made the day before in it to "bootstrap" the culture, and off you go. But lassi going with every meal is, to my knowledge, a characteristically north Indian/Pakistani thing.
Mangoes (assuming you mean ripe ones, not green) are a summer thing, and you do find roadside stalls doing "mango lassi" as part of their lists (which are impressive for their length, in addition to being $deity-sends when preceded by a suitably exhausting experience on public transport). I have the feeling, though, that it's probably something one is more likely to find outside of India.
(I'm from Kolkata, btw. Thanks for the chance to go on this unintended happy-rant.)