I have seen this question asking why the pronunciation, but I am more wondering where it varies. Is it only in São Paulo? Listening to pronunciations on forvo, it seems to be a 50/50 mix of pronouncing it both ways.
I am by no means a specialist in phonology, but as a native speaker from São Paulo, it seems to me that these pronunciation patterns you're mentioning (which are called "palatalizations") are more characteristic of the accents from Rio de Janeiro and São Paulo than from anywhere else (especially São Paulo). However, since most of the Brazilian mainstream media is located in these two cities, and since they are the most populous metropolitan areas in the country, they tend to be widely reproduced in music, television, and so on, so chances are you will hear them more frequently than not, at least in Brazil.
That doesn't mean that people from other locations don't palatalize /t/ or /d/, but palatalization doesn't tend to occur as consistently in other areas. For example, in the state of Paraná, people may often palatalize /te/ and /ti/ when they are stressed and not palatalize them when they are unstressed. This varies a lot from region to region, and it would be difficult to summarize the patterns according to geographic locations, but as I said, consistent palatalization seems more common in the accents of São Paulo and Rio.
One last thing: when /de/ and /di/ are palatalized, they usually sound like a "djee" sound, not a "ch" sound. At least I've never heard anyone pronounce them that way.
In Brazil, with regional exceptions (South and Western Rio Grande do Sul, Recife and adjacent areas), the palatalisation is mandatory when it is written "ti" or "di". If it is written "te" or "de", it only happens if the vowel is "reduced", ie, if it sounds like a very short /i/.
Bom dia - /bõw dʒiɐ/
Deus lhe pague - /dews ʎi 'pagi/
Boa tarde - /bowɐ 'tardʒi/
(As for the exceptions, in Rio Grande do Sul the vowel is not reduced, ie, we say /boa 'tarde/; in Recife, the consonant is rather "dentalised" - /boa 'tarði/ (which I suppose is a common pronunciation in Portugal, too).
The palatalisation may or may not occur in quick, careless speech, where final vowels are often elided:
Boa tarde, senhor - /bowɐ'tardse'ɲor/