Yep, just announced earlier today at WWDC.
http://www.apple.com/pr/library/2009/06/08iphone.html
From the release:
"iPhone 3G S offers incredible speed and performance, on average up to twice as fast as iPhone 3G, so you can render web pages quicker and launch applications faster. iPhone 3G S takes advantage of the OpenGL ES 2.0 standard for stunning high-quality 3D graphics, making mobile gaming and other graphic intense applications better than ever. iPhone 3G S is not only faster, but with longer battery life you can watch more videos, listen to more music, browse the Internet or keep using your favorite apps even longer. The new iPhone 3G S also supports 7.2 Mbps HSDPA for faster networking speeds.*** "
Sounds like a boost in CPU too (claimed up to 2X speed in a lot of applications - not sure what that translates to in terms of processor speed improvement.