Here are some universally accepted telephone manners that are expected from each and every person in the professional world. This list is not comprehensive, but nevertheless, it covers most areas of telephonic communication:
During the call, do not multitask. Even if you are working on something when the call comes in, stop everything and concentrate on the voice on the telephone.
Do not read, chat on instant messengers, or eat while you are engaged in a telephonic conversation. In IT organizations, I have witnessed many professionals do these three activities the most while they are supposedly speaking to someone on their telephones.
The tone of your voice must be pleasant and friendly. Even if you are bored to death or tired to slumber, cheer yourself up and be the friendliest voice one can hear on the other side.
Your body language has a say in how your voice tone comes out. When you are taking a call, sit upright and the confidence is showcased...