Through the Android Callout question type and some light custom XML CommCare is able to prompt telephone calls during form entry.
1 Add an Android Callout question
2 Select the "Custom" option under External App and enter ID android.intent.action.CALL
3 Open the "Edit Source XML" pane from the hamburger menu next to the app title:
4 Locate the <odkx:intent> definition block and add a "data" parameter containing the telephone number you want to call, preceded by tel:(this is to the Android specification)
<odkx:intent xmlns:odkx="http://opendatakit.org/xforms" id="call" class="android.intent.action.CALL" data="tel:1234567890" />
5 (Advanced) as of CommCare Android 2.42 you can use the output of another question as the telephone number to call. To do so, change the step from (4) slightly:
<odkx:intent xmlns:odkx="http://opendatakit.org/xforms" id="call" class="android.intent.action.CALL" data="cc:xpath_key:concat('tel:', /data/phone_number)" />
Where `cc:xpath_key:` is a key that tells CommCare to process the data as an XPath, while the `tel:` portion is explained above.