When it comes to work, you need to think about how you present yourself on the phone and in person. Most of the time you are going to have to make a lot of phone calls regardless. It is the phone call that will make a good impression. If you are too short with them they could think that you aren't a good person to deal with, but if you hold on to them too long, you may end up looking like an idiot. You need to find your medium.
When it comes to putting callers on hold you need to get their permission. This means that you should tell them that you need to get something important in order to help them or transfer them. You will then want to tell them what you are going to do and that it should only be a few moments. People hate waiting, so never leave someone on hold for long periods of time (five or more minutes).
If you are answering the phone knowing that someone has been on hold while being transferred you will want to thank them for waiting and then asking them how you can help them. Don't forget that you will have to introduce yourself as soon as you answer the phone. Keep in mind that they may be hostile, depending on how long they have been on hold, you will want to make sure that you do everything you can to assure them that it was an accident and it won't happen again.
As for transferring a call, you will need to tell them that you are transferring them and to hold on. You will also want to tell the person their number incase they get disconnected. You will also want to do this while keeping in mind that people really don't like being pushed to person to person. You need to do this with much poise and respect. It is important for customer service factors that you always show courtesy to the customers.
There are a lot of things that you will want to do when it comes to the phone, however, make sure that you think about the first impression that you are giving. You may need to adjust your voice, your volume, or the words that you use when on the phone. Keep in mind that you can't see them and they won't be able to get the non-verbal messages that most people will pick up when talking in person. This means that you will want to say what you mean and mean what you say.