First of all, yes, everyone on Twitter now should have access to the new Retweet functionality.
Currently, only Twitter.com and a handful of clients support the new mechanism.
But did you know that you can also trigger the new Retweets via SMS?
As the Twitter mobile account noted earlier tonight, if you simply send "RT USERNAME" to 40404 (at least in the U.S.) it will automatically retweet the last tweet of whatever username you entered has sent.
Regardless, Twitter's quick moves to expand and extend mobile support is pretty impressive.