When I press 1 to accept nothing happens

I get a call from a friend in PA state prison. There are many times the call comes through and when I hit 1 to accept the call nothing happens. It wont allow the call to come through. But then on some days it will accept the call. I have restarted my phone and I still can't get the system to recognize I hit 1 to accept. WTF and why is it only sometimes. my friend thinks I'm ignoring him!