Article in English: You can find them in  your contact list, or simply use the keypad to dial the number. When that call is established, tap Add Call. The first caller is placed on hold. Again, you can use your contact list, or just dial the number. This will add the second participant to the call.  You can conference with up to five people, depending on your carrier. This method works with both Apple iPhones and the Android HTC Hero.

Summary in Vietnamese:
Gọi một trong những người sẽ tham gia vào cuộc gọi hội nghị. Gọi người tiếp theo. Chạm vào Merge Call (Kết hợp cuộc gọi).