Aptela offers a robust conference option, but for simple 3 way conferencing you can use the Conference button on the Polycom or Aastra 6757i CT.

1. While on any call, press the Conference option on the phone (on some it's labeled 'Confrnc' or 'Conf'). At this point the party you are talking to will be put on hold.
2. Enter the phone number (if you want to conference in to a regular phone) or extension (if you want to conference in another user in your account). For extension, you need to use the '7' option - for instance, if you're trying to get x101, you would key in '7101', just like you were dialing that person's extension.
3. When the 3rd person answers you and they will be connected. To complete the conference, press Conference again. This will now connect all three.
4. To end conference call, hang up the phone or press 'Split' or 'Drop' to continue with one of the two parties.  After pressing Split you will need to pick up the line that is on hold.