The WTAI specification defines a core set of capabilities that all WTA user agents embedded on the mobile handset must support. These capabilities are defined as listed here:
The WTAI features are partitioned into a collection of WTAI function libraries. The type of function and its availability determines where the different functions are specified. The WTAI function libraries are accessible from WMLScript using the scripting function libraries. Some WTAI functions are also accessible from WML using URIs.
WTA services can place, receive, and terminate voice calls and can get information about voice calls. An implementation may support multiple simultaneous voice calls or may limit the WTA service to only one voice call at a time.
WTA services can send and receive network messages and can get information about network messages.
WTA services can access and modify the device's phone book.
WTA services can access the device's call history. The WTA user agent may provide access to the following call logs: Dialed Call Log, Missed Call Log, Received Call Log.
WTA services can access the device's logical indicators such as display indicators for a voice mail message or an incoming speech call.
This set of capabilities is divided between three classes of functionality:
Network Common WTAIaccessible only from the WTA user agent
Network Specific WTAIfeatures available only on certain types of networks
Public WTAIsimple features that are available to third-party application developers
We'll focus primarily on Public WTAI functionality here, but I'll briefly discuss Network Common WTAI as well.