FY2003

How do you read "FY 2003"? "Fiscal year 2003"?

Yeah, or say the letters.

What about "3.3 V"? Can we also just say the letter?

Anyone who knows that "3.3 V" means "3.3 volts" should say it that way. Otherwise they sound very naive.

For "FY", I've heard it both ways, just the letters and "fiscal year", even by knowledgeable people. I assume they say the letters just because it's quicker.

I'd say "Volts".