The WTAI not only defines URL schemes for making phone calls, but it also defines public functions you can invoke in WMLScripts. WMLScript requires the WAP gateway (or precompilation), so it is not as easy to use as plain URL links. On the other hand, WMLScript allows you specific logical conditions for making calls, and it makes it easier to handle the call status return value. For more information on WMLScript programming, check out W3Schools' WMLScript tutorial at http://www.w3schools.com/wmlscript/default.asp. The following WMLScript statement makes a phone call to number 5551234 and stores the return value in the flag variable:
var flag = WTAPublic.makeCall ("5551234");
If the call is successful, the return value in flag is an empty string. If the phone number is not formatted correctly, the flag value is invalid. If the call fails, the return value is one of the error codes.
The makeCall function call blocks, and it will not return until the call is finished. Hence, your browser might freeze when you are making a call via WMLScript.
In the previous example, the phone number is hardcoded into the URL. This is not very convenient in many scenarios. For instance, you might want a drop-down list of local numbers to choose from, or you might want to be able to enter your own target numbers. With a little help from WML variables, you can easily make the call link dynamic. The following example shows a WML text entry box. You can enter any phone number in the box and then click the link below it to make the call
Download here
In the example, the phoneno WML variable captures your input in the text box. Then its value, $(phoneno), is embedded in the phone call URL as the phone number. If you enter an incorrectly formatted phone number (e.g., alphabetic letters with numbers), the browser will throw an error when you try to make the call.
You might have seen how you can click a link to dial your phone from your wireless operator's 411 service portal page. But how does this work? Well, the process is really easy, with a special WAP interface known as WTAI.
One of the coolest features in WML is its support for telephony functions known as the Wireless Telephony Applications Interface (WTAI). A Nokia WML browser allows users to make phone calls, send touch tones, and update the phone's Contacts list directly from a web page! Since the mobile phone is still primarily a voice communications tool, the ability to integrate the telephone experience with the web-browsing experience proves to be very useful. You can do that with either specially formatted URLs or WML-Script function calls.
You can "link" to any telephone number via a specially formatted URL from your web page. Once you click that URL, the phone prompts you to make a call to the specified phone number. The URL can be embedded in a or a element in your WML, XHTML MP, or plain HTML pages. The following example shows an XHTML MP page with a phone call link:
Download here
The number +15555551234 after the wtai://wp/mc; string in the URL specifies the phone number. You can use any phone number format that your phone and wireless operator can understand.
When you click the link and confirm the message, a call to the specified number is initiated. Once the call is connected, the phone goes back to the browser and you can continue browsing while staying on the phone. The small phone icon at the top-right corner of the last screen indicates that a voice call is in progress. Although the screen-shots are taken from a Series 60 device, the process is similar on Series 40 devices. On a Series 40 device, you are given an additional choice to quit the browser before the call is initiated.
If you are browsing over a GPRS connection, the connection is suspended while the phone call is active.
