"...a Braille calculator. That is a calculator which speaks."

Eh??? Braille is a tactile interface - not spoken!

But surely, if you're doing Braille and speech you must have a microcontroller (or microprocessor) in there already - the calculator bit should be trivial.
Adding a separate calculator chip will just add extra component cost, assembly cost, inventory cost, etc, etc - and you'll still have to write the code to interface it to the rest of the system!