Google ANDROID 2.3.4 - Manual (Page 93)

Placing and receiving calls 93
AUG-2.3.4-105 Android User’s Guide
3 Place the next call, using the Phone tab, the Call log, or your contacts.
4 When you’re connected, touch Merge calls.
The participant is added to the conference call.
You can add as many callers as your carrier supports.
During a conference call, touch Manage to drop a conference call participant or
to talk privately with one of the participants.
End a conference call and disconnect all callers
S Touch End.