I don't think Smith is a mouth piece. He's a program in the Matrix and has a specific purpose like every other program. His job is gate-keeping. Like all agents Smith ensures humans hacking into the Matrix are located and terminated. He's specifically tracking Morpheus to get to Zions location. Now this is his purpose as a program.
But unlike the others he goes out of character .. specifically in that scene where he's talking to Morpheus..
Smith is a program. Programs, in the Matrix, have a function and they
perform their function. Smith seems be an anomaly. He expresses
frustration like human. He wants to move on from the Matrix, from his
function. He bypasses his programming to disconnect himself from
communication (removing his earpiece is indicative of that). This odd
behaviour is picked upon very well in the next two films.
Source - Matrix Explained
Smith has revelations, he gets frustrated, he wants to get "free", he talks of "smell". As a program he seems to tread beyond his space of operation. He clearly behaves differently from all other agents we are shown in the movie who are emotionless.
In the end of the Matrix we see Neo destroying Smith. But he returns in the second part saying this:
You destroyed me, Mister Anderson. Afterward, I knew the rules, I
understood what I was supposed to do but I didn’t. I couldn’t. I was
compelled to stay, compelled to disobey. And now here I stand because
of you, Mister Anderson, because of you I’m no longer an agent of the
system, because of you I’ve changed – I’m unplugged – a new man, so to
speak, like you, apparently free.
Source - Matrix Reloaded Script
Exiles are defined as programs that disobey deletion. Smith starts off as an Exile but he's far more than that. He is a virus (ironically) in the Matrix. He is taking over everything and the Machines are helpless, they can't stop Smith.
Neo: The program ‘Smith’ has grown beyond your control. Soon he will
spread through this city as he spread through the Matrix. You cannot
stop him, but I can.
Source - Matrix Revolutions Script
Clearly the central AI has no control on Smith and that's why Neo's deal is honored. Back in Part 1 when he talks about being the cure, it's part of the same conversation where Smith displays un-agent-like behavior. Considering this, we can say that Smith here was acting on his own. He was not a mouth piece.
Besides, it is revealed in Reloaded that the machines already knew the location of Zion. They don't need Smith for this. The machines are the ones who set up Zion in the first place with the help of the previous anomaly (The One). Smith's conversation with Morpheus a micro event for the central AI to be controlling word to word. Smith is clearly exhibiting exile tendencies in this scene, and we can say that those are his words, his perception.
By the way ...
The surviving bots along with supporting humans find exile in a new
nation they call Zero One. Zero One prospers and they develop further
generations of AI. The remaining human nations suffer.
Zero-One is not the name of the central AI, it is the name of the machine city.