Too bad it is only available in Norway, although some leaked version seems around on the Internet.
The Opera Mini technology, which is based on Java 2 Mobile Edition standards, is meant as an alternative to the Norwegian company’s regular mobile browser. The Mini targets the 700 million low- and mid-tier Java-capable phones worldwide that are currently incapable of running a web browser, the company said.
No one starts to use “Java ME” yet …
A lot of small sites that can fit on your phone:
Froogle now has its WML version. So next time when I am in a bookstore, I can point my phone’s browser to wml.froogle.com and compare price directly. It is so easy for books because I only need to input the ISBN number. Type 0131405306 and find a good deal on Michael Yuan’s Enterprise J2ME. 
Opera Browser got a lot of attention in the mobile world recently. It has been chosen by Nokia, Sendo and BenQ and will be the standard browser on their Symbian phones. Opera Software and Motorola’s Personal Communications Sector (PCS) just signed a licensing agreement to deliver Opera’s Internet browser on multiple Motorola PCS handsets.
Unlike other browsers on the phone, Opera tries to bring the full Internet experience to mobile devices. It supports not only markup languages specially designed for phones, but also many specs for PC browsers such as HTML, XHTML, CSS and JavaScript. Its Small-Screen Rendering technology automatically makes a more device-friendly version of the existing Web pages.
I did not find special emulator from Opera to test Web pages for devices. But Opera claims that "the desktop and device versions of Opera are based on the same code". So theoretically I can test mobile pages using its desktop version. Some guides on Opera site actually show how to do that. I tried some WML pages, and not surprisingly, the Opera desktop version can render them! That is probably the only PC browser can show WML pages. One magic short-cut is Shift+F11 to switch to small screen mode. Opera Desktop also has a built-in HTML validator that helps you validate your pages for conformance to W3C Recommendations and standards. I still love Mozilla Firefox. But it is handy to have a PC browser to try some old WML sites.
A lot of terms: HDML, cHTML, WML1.x, XHTML Basic, XHTML Mobile Profile and WML2
The first Chapter of XHTML-MP Style Guide on Openwave Developer Network site clearly explains the history of those Wireless markup languages. Another wonderful overview online I found is Little Springs Design’s An Overview of Mobile Versions of XHTML.
Open Source Software for Mobile Phones