this is common among tamil speakers

Yes, I didn't mean to imply that it was some rare fault of my friends. Tamil only has one consonant for each of those four in Sanskrit/Hindi: p for p, ph, b, bh; t for t, th, d, dh; etc. I remember when I was learning the Tamil syllabary, I looked at a religious of my friend's mom's: I saw some Sanskrit transliterated into Tamil script. It was impossible to figure out what the Sanskrit words actually were. When I lived in Germany, I used to marvel at how many ways my name, Jim, could be pronounced, especially the j, but also the i. The m was pretty standard.

Ceci n'est pas un seing.