Qnewbie

Which way is lack of voice? Outgoing from intranet or incoming from outside?

1. Check RTP ports in both Elastix and router.
2. Put your Elastix to DMZ. What is the result?

Most likely, the port forwarding is not setup properly. Otherwise try this one:
3. Replace the router with another brand.

Qnewbie

There is echo test number in Asterisk. Dial 600 and you get echo test.

RTP ports are often assigned to 10000-20000 in rtp.conf.