Texting with android device & my iPhone

What happens when you try to text? Are you getting an error message? Can you send SMS messages to other people?

There are no options on an iPhone to turn SMS on or off. The only setting that mentions SMS is the one lets you request the phone send an SMS to an iMessage user if the iMessage fails. It would have nothing to do with sending an SMS to an Android user.

Did your son switch from an iPhone to an Android? If so, Apple's system may not be recognizing the change. Have him follow these instructions:

Deregister and Turn Off iMessage - Apple Support

You may also need to delete his contact information and any messages threads with him once he's done that. Then, add the contact information back.

There's nothing to "keep in reserve". He can't use iMessage from an Android phone even if the phone number is the same as his old iPhone. He should deregister as soon as possible or he's going to miss a lot of messages and have a lot of frustrated friends and relatives. Should he ever start using the iPhone again, he can turn iMessages back on for that phone number.

Tell him your going to start actually calling him if he doesn't get it resolved! ;-)

Good luck!