agree vs agreed

[Winwin2011]

My friend: I think that people who drive cars and use a mobile phone while they are driving, should be fined. What do you think?

1. Me: Agree. (I agree)
2. Me: Agreed. (Does "agreed" represent " I agreed"?)

Are the above sentences both correct?

 

[tedmc]

My friend: I think that people who drive cars and use a mobile phone while they are driving,(no comma) should be fined. What do you think?

1. Me: Agree. (I agree)
2. Me: Agreed. (Does "agreed" represent " I agreed"?)

Are the above sentences both correct?

I think they are both OK and understandable for spoken English.
The second would mean: The statement is agreed. (Not "I agreed")