My iPhone 5s which I bought a year ago shows "Call Failed" whenever I hit "send", it doesn't matter which number I'm dialing. I can get incoming calls, FaceTime calls, messages, and apps are working fine. I placed my SIM in another device and mananged to make calls, and I tried putting another SIM in my iPhone, and once again got the instant "Call Failed" message.
Is this more likely to be a software problem or hardware? How can this be addressed?