Several of my higher level students have asked me to help them to practice telephone conversation as it is very difficult not being able to see the other person when they are speaking. Seeing the person while talking certainly aids understanding. So to give my students practice in doing this, I have started to list up many situations in which a person working in various kinds of business may need to contact someone and speak English. I practice these with my students and teach them the new vocabulary words that come up in the conversations. Words like ETA, ETD, expedite, air freight, FOB, invoice, payment, RFQ, proposal, presentation, conference call, LCD projector, agenda, schedule, consignment, shipment, hotel reservation, file attachment etc. can be easily taught as well as how to ask questions for clarification when you do not understand what the other person just said.
Students really appreciate this kind of specific help that can make them better at their jobs. Many of them work for companies who deal with customers in English and many also work for US, UK and European companies where they need to be good at speaking English on the phone.