I had the same problem and quickly figured it out. you have to dial a number first, like 1 or area code or something to bring up the dialer screen. The top right corner shows 123. If you press shift it will change to ABC. Then you type out like normal. To change it back to numbers just press shift again and you will see it change to 123 again.
it will dial out the correct numbers it needs to when you press talk.
Check out a fun infographic that teaches you how to increase storage, enhance security, improve battery life and clean your device.