Its not tri service training yet for phase 2, I think that is still a long way off. The SIB course though is Tri service as are a number of others. Phase two hasnt really changed much at all over the past ten years apart from the fact that it has got easier (Im not just saying that either!) so just have a look at any of the RMP training threads already on here if you are not aware of what the training consists of.
Hey when i studied Military Law at uni. I found that the Army law and the RAF law merge more than the naval law. So I too think it will be a long time till you get tri service training as a Police Officer. However thinking about it a lot of the training will be the same. i.e arresting sumone and the rights etc... so there might be tri service training in that area, however learning law i don't think the will be. But feel free to correct me if i am wrong, i haven't studied Military Law for over a year now.