For sending SMS you need to compose an email with following parameters.
Subject (xxxxxxxxxx = DID)
Your text message.
In above example, we are sending SMS to number 1-949-471-0101 using DID 1-949-930-0360 from the email account associated with number 949-930-0360.
Incoming SMS :
All your incoming SMS will be forwarded to the email associated with you DID. You can also check SMS record in section Reporting ⇒ SMS.