How do I turn on text messaging in a custom campaign?

To turn on text messaging in a custom campaign, click on the "Text" step in the campaign designer and select "Send Text Messages with this campaign."

This will bring up the text window. You can type your message there. Note there is a character limit, and you must include the two merge fields for your practice phone and the SMS opt out message. 

The "from" name can be adjusted by visiting the Settings tab under "Phone and Text Message Settings."