- There are no characters for aspirates.
- A single character is used for both voiced and unvoiced sounds. E.g., the character க represents the guttural sounds 'ka' and 'ga' (and also 'ha'). The character ச is used for the sounds 'ca', 'ja' and 'za' (and sometimes 'Sa').
But not anymore. A large fraction of the current generation of Tamil-speakers bear names that are Hindi-like. Venkatesh (veGkaTez) where the traditional version would have been Venkatesan. Shankar as opposed to the traditional Sankaran. Satish or Akash, which were never prevalent in the previous generations. And there is no Tamil character which can unambiguously represent the za sound.
As of now, we make do using ஷ (Sa) which is not the same sound at all. I feel time is ripe for Tamil to make space for one more character from Grantha () to represent za. (In fact, this character is already present in Tamil in the symbol for zrI.)
However, given the anti-Sanskrit leanings of Tamil scholars, I am not sure if this will happen.