Cisco IP Phone at Home-No Voice

we have configured Cisco Ip phone at home with our external TFTP address and it works fine,..It was working fine, but now when users call from home  IP phone , the dialed party cannot hear the voice of the caller and vise versa...can you please let me know, wht seems to be causing the issue, as the call is getting conencted , its just that there is no voice.

is it a Call Manager related issue or Firewall or something else..Please advise
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fshaikh1234Connect With a Mentor Author Commented:
figured out that the ISP had blocked voice over IP..problem resolved
I also am facing this exact problem. I
have not began troubleshooting but I will start by looking at the firewall logs to make sure there isn't a packet being dropped.  
the RTP packets (voice traffic) is going between two phones the call manager is not in between so the phones cannot ping each other because of this the voice will not pass.
the call is connected because the call manager is responsible for signaling and it can see the phones.

You will need to open some UDP ports on both firewalls. Start with ports 16384-16500. This should allow the RTP packets to negotiate the firewall.
try the mtp command under ephone
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