[SR-Users] 2 phones behind same NAT, Kamailio on Pub IP One Way Audio

This is my first go round' with Kamailio but I have been messing with it off and on for a few weeks. Running latest version on latest CentOS 7.x. Kamailio installed on VM with public IP in one location, 2 SIP phones behind same NAT, both registered to Kamailio fine. I can call one phone to the other and it rings and I can answer it but get one way audio most of the time, sometimes no audio at all. I just did a standard install with MySQL and no other modules. What am I missing, do I need RTPPROXY? Will Kamailio allow extension to extension calls from/to phones behind NATS without any additional modules? I tried installing it with yum, it installed but it won't start. If I need it, I will remove the YUM version and install from source or GIT or some other method. I do NOT want any media passing through this server, that's one big reason I am learning something OTHER than Asterisk which I am very familiar with. I see all these RTP modules, music on hold etc but I specifically don't want to install anything that causes media to pass through the box. Finding the learning curve much steeper than Asterisk back in the day and a REALLY tough time find step by step examples to get started, especially on CentOS. I bought the draft of the book and it will be a great resource but at the moment, it's not helping me get started or get my first instance up and running. I need to add SIP trunks to originate and terminate calls but I can't even think about that since I can't even get audio on extension to extension calls yet. I also see that Kamailio fails to startup at boot because it can't connect to MySQL, when I restart Kamailio it starts fine. I think the issue is that Kamailio is trying to start before MySQL is up and running, I guess I can do a delayed start of Kamailio to fix that later. Any help would be appreciate by this NEWB. Thanks in advance for any assistance.