I found this posted somewhere online:

Nonverbal autism is a form of autism that is characterized by a lack of or limited use of verbal communication. This can include difficulty using words to express needs or desires, speaking in single words or short phrases, and difficulty understanding language.

There are many ways available for your son to communicate:
-Signing/Sign Language
-P.E.C.S. (Picture Exchange Communication System)
-Buttons (Pre-Programed buttons with Words)
There's the 3 main ones.
The P.E.C.S. used on the Device(s) can even have 'Talk' Features like the 'Buttons'.