Line2 App for iOS: On-Call Options

Mute- 
Clicking this button will mute your microphone until you deselect it. Your party on the other line will still be able to hear you.

Add Call- 
 Allows you to add additional people to this call.  Click the add call button and type in a contact name or number hit enter to add them to the call.  You can add up to 20 people to a conference adding them one by one.

Hold- 
 Selecting this button will mute your microphone and speakers until it has been deselected. Both caller and receiver will not be able to hear each other if this is selected. 

Transfer- 
This button allows you to transfer the call to another number. Click the transfer button and type in the number you want to transfer to.

Keypad- 
Selecting this will display the on-screen keypad. 

Merge - 
Selecting this will merge your current calls into a conference, this is only available if you have 2 calls already connected.