Mobile App / Enhanced Dialer (Samsung Galaxy S6 / S7)
Open the One Talk app.
Tap the Keypadicon .
From the Keypad tab, enter the desired 10-digit number then tap the Phone icon.
Don't prefix the dialed number with a '9' as is currently required with a traditional PBX (Private Branch Exchange) system. If a '9' is accidentally added, the call fails and the caller receives an error recording.
Tap NewLine (lower-right).
From the keypad, enter a 10-digit number then tap the Phone icon .
Drag the preferred call to merge.
When the image below appears, both calls are in conference.