You can use almost any Ooma Office device to make internal calls between extensions.
The way that you will make an internal call depends on the type of phone you are using.
You can call another extension by dialing the extension number. Calling a remote extension places a call to the external forwarding number.
Cisco or Yealink IP phone
Pick up the handset or press the speaker key and dial the internal extension number.
Click the keypad icon () and dial the internal extension number.
Click the Settings button () and choose Keypad (). Dial the internal extension number.