to access the current call on hold.
<CallButtons>
...
<Button>
<title>Resume</title>
<action>RESUME</action>
<value></value>
<enabled>false</enabled>
<confirm>false</confirm>
<description>Resume an active call</description>
<bg_color>#FF001425</bg_color>
<fg_color>#FFFFFFFF</fg_color>
<icon>Default</icon>
</Button>
...
</CallButtons>