I have the same problem with brand new iPhone 6 plus, facetime and third party call app works fine only with cellular network i hear the static sound, I've tried every reset/restore. Apple dealer did hardware diagnostic and everything tested fine. SIM card woks fine on other device. So my guess it has to do with intervention between earpiece speaker and antenna. I had no accident with my phone, and it was working perfectly for 4 months before this happen. any advice? I tried changing speaker and cleaning the mesh, not working!!