Dial a number

Action: 
android.intent.action.DIAL
Input: 
If nothing, an empty dialer is started; else URI of a phone number to be dialed.
Output: 
None

Dial a number as specified by the data.

This shows a UI with the number being dialed, allowing the user to explicitly initiate the call.

The uri can be a tel: URI of an explicit phone number.

See Android documentation.