WAP is an open international standard for application layer network communications in a wireless communication environment. Its main use is to enable access to the Internet (HTTP) from a mobile phone or PDA.
A WAP browser provides all of the basic services of a computer based web Browser but simplified to operate within the restrictions of a mobile phone, such as its smaller view screen. WAP sites are websites written in, or dynamically converted to, WML (Wireless Markup Language) and accessed via the WAP browser.
 WAP 2.0
WAP 2.0 is a re-engineering of WAP using a cut-down version of XHTML with end-to-end HTTP (i.e., dropping the gateway and custom protocol suite used to communicate with it). A WAP gateway can be used in conjunction with WAP 2.0; however, in this scenario, it is used as a standard proxy server. The WAP gateway's role would then shift from one of translation to adding additional information to each request. This would be configured by the operator and could include telephone numbers, location, billing information, and handset information.
XHTML Mobile Profile (XHTML MP), the markup language defined in WAP 2.0, is made to work in mobile devices. It is a subset of XHTML and a superset of XHTML Basic. A version of cascading style sheets (CSS) called WAP CSS is supported by XHTML MP.
 WML Tags
WML is mostly about text. Tags that would slow down the communication with handheld devices are not a part of the WML standard. The use of tables and images is strongly restricted.
Since WML is an XML application, all tags are case sensitive (<wml> is not the same as <WML>), and all tags must be properly closed. WML Decks and Cards
WML pages are called DECKS. They are constructed as a set of CARDS, related to each other with links. When a WML page is accessed from a mobile phone, all the cards in the page are downloaded from the WAP server. Navigation between the cards is done by the phone computer - inside the phone - without any extra access trips to the server.
 Example WML document:
<?xml version="1.0"?> <!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN" "http://www.wapforum.org/DTD/wml_1.1.xml"> <wml> <card id="HTML" title="HTML Tutorial"> <p> Our HTML Tutorial is an award winning tutorial from W3Schools. </p> </card> <card id="XML" title="XML Tutorial"> <p> Our XML Tutorial is an award winning tutorial from W3Schools. </p> </card> </wml>
As you can see from the example, the WML document is an XML document. The DOCTYPE is defined to be wml, and the DTD is accessed at www.wapforum.org/DTD/wml_1.1.xml. The document content is inside the <wml>...</wml> tags. Each card in the document is inside <card>...</card> tags, and actual paragraphs are inside <p>...</p> tags. Each card element has an id and a title.
 For more information
http://www.w3schools.com/wap/default.asp - A tutorial