Once you have placed a call on hold, you can make a new call with another line. The way that you will do this depends on the type of phone you are using.
Analog phone
Listen for the fresh dial tone after you put the call on hold by pressing [Flash]. Dial the second number as you normally would. Your first call will remain on hold for the duration of your second call unless you resume it.
IP phone
When you have put the call on hold, press the button beside an unused line to bring up a fresh dial tone. Dial the second number as you normally would. Your first call will remain on hold for the duration of your second call unless you resume it.
Ooma DP1 desk phone
Press the unoccupied LINE button to bring up a fresh dial tone and dial the second number you would like to reach. Your first call will remain on hold for the duration of your second call unless you resume it.
Ooma desptop app
While you have an active call in progress, click the Make Call button. The current call will be put on hold and a fresh dialer window will appear. Dial the number or a select a contact you would like to reach. Your first call will remain on hold for the duration of your second call until you resume it.