From page 13 of the OBi Device Administration Guide (OBiDeviceAdminGuide.pdf):
3-Way Calling
3-Way Calling allows you to talk to two parties at the same time with everyone on a telephone at a different location. To use 3-Way Calling, when you are in a call with another party and want to add a second to the conversation, press the "flash" button or depress and release the switch hook on your phone. You will be presented with a second dial tone and the first party will be placed on hold. Dial the second party. When they answer, you will be able to inform them that you intend to connect them with the first party (now on hold) and have a conference. At this point press the "flash" button or depress and release the switch hook on your phone. This will connect the first party, the second party and yourself. You can all continue to talk together.
Call Transfer (Attended)
You can transfer a call to a third party using the attended transfer capabilities of the OBi. To use Attended Call Transfer, while in a call with the party who will be transferred, press the "flash" button or depress and release the switch hook on your phone. You will be presented with a second dial tone. The party who will be transferred will be placed on hold. Dial the transfer target. When the transfer target answers, you will be able to inform them that you intend to connect them with the party on hold. At this point press the "flash" button or depress and release the switch hook on your phone. This will connect the party to be transferred, the transfer target and yourself. You can continue to talk together, as this is now a 3-way call, or you can hang up the phone and the other two parties will remain connected.