Hi, thanks for all advice. Son very sheepish and upset this morning. Upset that we were upset and disappointed. Had a long talk about it all. Upshot being that he knows all this stuff was inappropriate and horrible, but I do think there's a lot of egging on and bravado from all of them. On re reading his phone, at least he was saying the porn on the other boy's netbook was "disgusting" and "horrible" (not excusing anything he's written, by the way).
As regards our baby, and his feelings towards that, he has been so excited about it, talking abou it a lot unprompted and positively at home, although I was worried nearer the start of the pregnancy as he had one tearful bed time when he was worried about being "replaced". But he said he has had a lot of teasing about me being pregnant at school, so felt "like he had to just answer back", which sort of makes sense at a push.
Anyway, I've kept the phone, he accepts he's not getting it back for a while and we will be checking it when he does. Other than all this, I think we're just going to leave it alone now, and just be as vigilant as we can; obviously can't police what they actually say to each oher at school.
On the plus side also, he has lots of normal friendly text conversations with girls and boys, so I don't think he really has a horrible attitude towards girls.
Sorry if this is a bit rambly and incoherent; I'm exhausted, didn't sleep well last night.
Lego making, football loving, child who loves Wallace and Gromit and has teddies versus these text messages is difficult to understand.