It's just reassuring that he is able to call me when and if he needs to without needing permission from his minder. To be honest we don't even use it that much, it's just something that makes me happier. I posted here before I got it to find out what options there might be to keep tabs, and this was suggested.
Of course I know pretty much where he is when he's outside - he is allowed to play on teh green but it is quite a large area. And he of course checks into the house regularly when he's outside playing in the summertime, and isn't allowed into anyone's house. In the winter it's not even an issue, they are either at home or at an organised activity like sport.
At the same time, I'm a single parent, working fulltime and studying part time, and also trying to decorate a house on my own - we're not together as much as I'd like, there is only so much one person can do, and this is a little link for us.
edited to add: I don't think the school has a rule on phones, if they do I'm not aware of it. He does make sure it's switched off during the schoolday, and of course the beauty of the firefly is you control the calls in and out, so only family and his minder for example are allowed to call it and they know he is in school...