You can talk to more than one person at a time, and merge up to five calls, depending on your carrier.
NOTE: Conference calling may be an optional service in some countries. Contact your carrier for more information.
Make a call.
Tap Add Call and make another call. The first call is put on hold.
Tap Merge Calls. The calls are merged on one line and everyone can hear each other.
Repeat steps two and three to add up to five calls.
Tap Conference and tap
next to a call. Then tap End Call.
Tap Conference, then tap Private next to a call. Tap Merge Calls to resume the conference.
Tap Hold Call + Answer, then tap Merge Calls.
If your service includes conference calling, iPhone always has a second line available in addition to the conference call.