Here is some advice for ESL learners about speaking in English on the phone.
Speak slowly and clearly
Listening to someone speaking in a second language over the telephone can be very challenging because you cannot see the person you are trying to hear. However, it may be even more difficult for the person you are talking with to understand you. You may not realize that your pronunciation isn't clear because your teacher and fellow students know and understand you. Pay special attention to your weak areas (such as "r's" and "l's" or "b's" and "v's") when you are on the phone. If you are nervous about using the phone in English, you may notice yourself speaking very quickly. Practise or write down what you are going to say and take a few deep breaths before you make a phone call.
Make sure you understand the other speaker
Don't pretend to understand everything you hear over the telephone. Even native speakers ask each other to repeat and confirm information from time to time. This is especially important if you are taking a message for someone else. Learn the appropriate expressions that English speakers use when they don't hear something properly. Don't be afraid to remind the person to slow down more than once. Keep your telephone in an area that is away from other noise distractions such as a radio or television.
Practise with a friend
Ask another student to practise talking on the phone with you. You might choose one night a week and take turns phoning each other at a certain time. Try to talk for at least fifteen minutes. You can talk socially, or role play different scenarios in a business environment. If you don't have access to a telephone, you can practise by setting two chairs up back to back. The most important thing about practising telephone English is that you aren't able to see each other's mouths. It is amazing how much people lip-read without realizing.
Use businesses and recordings
There are many ways to get free telephone English practice. After business hours, you can call and listen to recorded messages. Write down what you hear the first time, and then call back and check if your notes are accurate. Use the phone in your everyday life. Call for a pizza delivery instead of going out to eat. Call a salon to book a hair appointment. You can even phone the movie theatre to ask for the listings instead of using the newspaper. Some large cities have free recordings you can call for information such as your daily horoscope or the weather. (Make sure that you aren't going to get charged for these numbers first.) Some products have free phone numbers on the packaging that you can call for information. Think of a question you might want to ask and call the free number! For example, call the number on the back of the cereal box and ask for coupons. You will have to give your name and address. Make sure you have a pen handy so that you can repeat the information and check your comprehension.
Learn telephone etiquette (manners)
The way that you speak to your best friend on the phone is very different to the way you should speak to someone in a business setting. Many ESL speakers make the mistake of being too direct on the telephone. It is possible that the person on the other line will think that you are being rude on purpose if you don't use formal language in certain situations. Sometimes just one word such as "could" or "may" is necessary in order to sound polite. You should use the same modals you would use in a formal "face-to-face" situation. Take the time to learn how to answer the phone and say goodbye in a polite manner, as well as all the various ways one can start and end a conversation casually.
Practise dates and numbers
It only takes a short time to memorize English phonetic spelling, but it is something that you will be able to use in any country. You should also practise saying dates and numbers aloud. You and a friend can write out a list of dates and numbers and take turns reading them over the phone to each other. Record what you hear. Swap papers the next day and check your answers.