SIP sets behind CISCO firewall connecting to public IP

[JDCre63]

I installed a Yealink T48G on the end of a customers cable ISP connection without any router or firewall, programmed it properly and it came and worked. Problem became that anonymous SIP calls, strange non-user induced forwarding would occur, et., so I decided to install a CISCO RV042G router. I figured I had to do a NAT from public to private but the RV042G wouldn't allow me to set the NAT up with only a single public static IP. Had the customer get a static block and will re-attempt to get it to set up behind the router so it has some firewall protection.

Can anyone point me in the right direction to setting up a SIP phone behind a CISCO router when that SIP set is NOT part of an on site IP/SIP PBx but connected directly to the ISP?

 

[nyy1023]

One of the things that is needed to be understood is the ports being used in the call set-up and registration. If you are on the outside of an appliance and unrestricted and now going inside the network it is possible that the ports are being blocked.

Couple of questions:
1. What happens when you connect a workstation or laptop to the router, does it work?
2. Does the SIP client get an IP address from the router? If so, is it on the same subnet as the laptop?

I am looking through the following document:

http://www.cisco.com/c/dam/en/us/td/docs/routers/csbr/rv0xx/administration/guide/rv0xx_AG.pdf

Seems to have some of what you are looking for.

CCNA, CCNP