My nephew is a voracious reader and his folks got him a kindle fire. They want to let him text (they have a wifi gateway service) but only with some people - a short list of phone numbers. Any ideas? Did I miss a doc page somewhere?
As the Kindle Fire only uses WiFi for web access, not a cell carrier, it does not normally have the capability of texting another cell phone.
It does have the capability to access websites that do texting, where the only parental control solution is to use Setting Parental Controls on Kindle Fire. I have no idea how effective these controls are.
You could also use an application such as the free textPlus (minimum age to use is 13). But the only control you would have is to keep a copy of the logon and password and ensure that the child knows you have it and that you will be looking (and threaten him to hell if he changes it).
But it's certain that sooner or later the child will escape your vigilance, should he wish to. Self-discipline is the only long-lasting solution.
Sending SMS messages is a function of the mobile telephone networks (though it's lately been extended to VoIP networks as well). It's not possible to send them from a device not on one of those networks without going through a gateway of some sort, such as an email to SMS gateway, and usually such gateways are one-way only, making a conversation difficult or impossible.
If he only needs to be able to talk to a specific list of people, an instant messaging app such as imo might be more appropriate.
If you're willing to dig around a bit, you can find a copy of the Google Voice for Android app and use a Google Voice account for sending and receiving SMS. Google distributes this app only through Google Play Store, which means you would have to copy it to the Kindle Fire from another Android device. This is not guaranteed to work, of course, though some people have done it successfully.
While this is only a partial answer, it should give you some direction for further investigation and hopefully you'll find something you can work with.
As we now know what app you are using for texting (Text plus), I can provide you with a somewhat acceptable answer.
But as a kinda young person, I must ask you: why? the texts are unlimited and free, what can go wrong? him talking to his friends more? Anyway, you do as you wish, it's your child...
The only way you could do a kind of what you want is go the opposite route. The only thing that is possible with the Text+ app is blocking user. Blocking a user means never agains being able to message him and never agains being able to receive message from him. You can do that fairly easily in the app, and you can go on and look at his kindle everyday or something to see if he sends a message to someone else and threaten him to block the number if he does. His friends / people he text with won't be able to change sms number that frequently.
For additional information about security in the Text+ app, you can look here
Unfortunately I cannot find any apps that have parental blocking for numbers.
I think you would be better off getting the kid an actual phone which can be configured to use fixed dialling numbers
That way you can safely limit who he can contact,who can contact him and get none of the downsides of using an sms gateway such as needing to be in range of a wifi hotstop to contact anyone.
Try looking for mobile phones designed for kids as these often have features you might be interested in.
I know this doesn't exactly answer your question but I could not find anything else that would be appropriate for your needs. You might be better served asking this on the android stack anyway.