Kindle Keyboard (aka Kindle 3) is a wonderful e-reader but it does not provide a very good internet browsing experience. The e-ink display just doesn't work well for scrolling and zooming, which nearly every website requires on such a small display. Although I haven't tried it, Google Reader probably would not be satisfactory. The Kindle Keyboard's web browsing functionality should be considered for emergency use only. My iPhone provides a much better browsing experience.
You can read RSS feeds for free on the Kindle Keyboard using Calibre, a PC program that can convert RSS feeds into e-book format for Kindle or other e-readers, and will download them to your Kindle. Then you can read them in Kindle's magazine format, which will use proper sized fonts and paging that works well on the Kindle.
Kindle Keyboard 3G service uses AT&T in the US and is free. It is used primarily for ordering and downloading books using an Amazon book browsing app on the Kindle, and for receiving books that you order on Amazon's web site through your PC or other internet device. It uses very little bandwidth, so Amazon gives you the 3G service for free. The "experimental" web browser is so clumsy to use on the e-ink display that you'll end up not using it much. The newer Kindle Touch only allows book ordering and Wikipedia browsing over 3G, it does not allow unrestricted web browsing, presumably because the touch display would make web browsing so easy that the usage would exceed Amazon's ability to provide free 3G service.