It's time to look Alexander Graham Bell in the eye (well, figuratively), and pick up that phone.
1. Practice, practice, practice! Call restaurants and ask them their hours. Call retail stores and ask them if they have a particular thing in stock. Call when you know someone you're comfortable with is not available so you can practice leaving voicemails. Call numbers that have voice activated systems and don't cheat and use the keypad option! The more you practice for the sake of practicing, the less stressful it will be when you actually have to make a phone call because you will know what to expect.
3. Know what you're about to say! This does not apply to all conversations, however having an idea of what you want to say and jotting it down when possible can help! You can especially do this during your practice calls. I have my students write down the questions they are planning on asking and either underline some words to voluntary stutter on or underline some feared words to act as a reminder to use their speech tools (i.e. cancellations, pull outs, prep sets).
You can start practicing on this site! Click on the "voicemail" tab on the right and leave me a message. Practice advertising and tell me a little about yourself and your stuttering!