Is there any way to have my son's phone set to where any text message that he receives or sends comes to my phone too.
I use DeskSMS on my phone, which will forward all texts to an email address of my choosing (which could then be received on another phone) and also allow responding through email, but it will appear to that person as a standard text from your phone. I found it really handy when I was working in a secured office that didn't allow personal cell phones. I could leave my phone in my car and still be notified of any texts and still respond to them, and the person wouldn't have any idea I was using email to respond.
In using it on your son's device, it is relatively easy to disable, so if your son doesn't want you to see things and is technologically inclined, he could probably find ways around it. But I think if the kid is smart enough, just about any app is able to be bypassed. It isn't made for monitoring, but it would work just the same.
I believe there is a $5 yearly charge (I am pretty sure it comes with a 30 day trial), because of the costs involved in running the server that processes everything.
Not exactly to your phone, but there are several "child care" apps available in the playstore which can be used to monitor activities. Take e.g. a look at Care4Teem, Best Parental Control Android, or ParentalFlux Parental Control. Most of these kind of solutions offer a dashboard on the provider's website, where you can check logged acitivities such as calls, messages, etc. Some additional monitor the location and even allow for "geo-fencing" (sending you an alert when the kid leaves the "permitted zone").
Yes, you can spy on your son's phone without him knowing with the help of mobile tracking software. I have been using this spying app for watching my kids to be sure that they are where they supposed to be. Through this tracking app you can spy on his text messages, calls, every activity on his cell phone. Another thing regarding privacy - as you are really concerned about your son and you take care of him, you have the right to monitor his SMS messages. I think software will help you.