I thought this guy was gonna be in the show, thats why they introduced him in the webisodes. He was locked up in level 5 in the last webisode and now no mention of him in the real season.

I heard they were going to do this (to be honest, I never saw much point to the webisodes at all) but for whatever reason, they decided to replace Echo with someone else who is on Level 5, with the exact same power- Jesse Murphy)

I don't why they did this, as Jesse just ended up getting killed by Sylar, and come on, Sylar is far too addicted to telekinesis to bother using the sonic scream, so that was a waste (for that matter, when will Sylar ever bother to use Clairsentience OR Alchemy?). Echo would have been a far better option IMO. He could have joined Pinehearst along with Knox

Actually Echo WILL be appearing in Episode 13 of Heroes. It was stated in an interview "Behind the Eclipse" with some of the show's writers.

He is scheduled to appear in the episode titled "War"

I really didn't see the point of the webisodes either, even though it was some Heroes. It was not the same. And I agree, Sylar is never, ever (maybe once) going to use his sonic scream, and to be honest, I really don't see Sylar using the sonic scream, I don't think it fits him. It fits Peter though

But, Echo was a fair character to me, would be cool to see his role in the main series.