1. I'm 5' 10" - most often you will hear people say "I am five ten" and that's it. Even here in Canada we are still using feet and inches and confuse a whole pile of people who don't know the old system.
[I]2. I'm 5 Foot 10"...[/I just another informal way of saying the same thing. The singular form "foot" is used a lot when talking about people's heights.
3. I'm 5 Feet 10 inches tall - is perfectly OK.
BUT in #2, Why can't we say, I'm 5 Feet 10" ??? Since FOOT is plural
we can and we do.
Also, singular forms are used as modifiers before nouns in plural measuring expressions:
"I am a five foot tall man".
in #3, Why can't we say, "I'm 5 Foot 10 inches tall?? - a little long but perfectly fine.