sim card wont read

I am getting an error message when I put in my sim card into my phone. I am trying to see what I need to do to get my sim card to work in my phone. the message is telling me your iPhone can not be activated because the activation server cannot be reached try connecting you iPhone to a mac or to a pc with iTunes to activate it or try again in a couple mins. I tried to do what its asking and I still cant get it to work. can someone help me with this. I cant not use my phone due to this matter.