Battlefield Modding Tutorials BFMODS

I uhm made a phone and its going to be part of a solider,yes a solider but I don't know how to attach it ,the solider is going to be invisible and when I attach it to the us hippack all you have to do it crouch and it goes underground and then obviously since the solider is invisible you can see anything ,so how can i make it so #1 it will collide with the ground and not go under or #2 attach it so it wont move down with the body,because it has to be at ground level ,thanks