No sound out

If I call out or someone calls in I can hear them but they can’t hear me?
I’m using cisco 7940 phones and evrything else appears to be working fine little help please

Some detail would really help otherwise its random guesswork.

  1. What version of Asterisk?
  2. What version of FreePBX?
  3. Do you use any distro like AsteriskNow or PBX in a Flash?
  4. What firewall do you use?
  5. Have you checked your logs from Asterisk?
  6. What kind of trunk(s)?
  7. Are you using NAT?
  8. Can you make internal calls from one 7940 to another OK?

Based on my experience, one way audio is almost always a network problem rather than an asterisk problem, but need more info to even start to think about this.