Phone calls with no answer...?

Okay so i am sitting here with my friend. she is sitting rite next to me and i then recieve a phone call. its from her and it says her name and everything on the caller ID. we check on her fone that is rite next to us and it doesnt say shes callling anyone. we pick up and no one answers. i can only hear myself saying hello on the line.

later, my friend recieves a fone call from me. only, i didnt call her. she picks up but again, she only can hear herself just like what happened to me.

any idea as to whats going on? best answer that we recieve the quickest will be chosen as the best