Calls work, but no sound

I thought I had this licked, but I guess not. I set up Asterisk and documented how in this how-to:
It worked just fine, but stopped a couple of days ago. Now when a call comes in or goes out, nothing happens once it’s answered. Neither end can hear the other end. The line remains open until one end hangs up. If I don’t answer the call goes to VM successfully and they can hear it just fine. When I call my VM I can get the message just fine. What the heck am I missing?

Describe your Asterisk setup. How do you connect to the PSTN? How does your phone connect to Asterisk?

Firstly, the ports would be blocked by ISP. Second, pls try to remove the firewall if u have.