Is there a product that will allow installation of 2 or more cable / DSL routers on 1 cable modem

What i am trying to accomplish is to add an proven acceptable VOIP router to a clients network that will allow me to install a voip phone without disrupting their existing router with security in mind Thereby having only the added VOIP phones in a NAT configuration only on this new Router

You should be able to simply add another router between the cable modem and the existing router.
Use a port on that router for the phone.

DISCLAIMER- I am not a CG so don't take my word for anything computer related.

-Hal

In order for us to help, you probably should provide a bit more information...it sounds like you are trying to establish a VPN with an IPsec router...is this the case?

Does the customer have a block of static IP addresses? If so, and the Cable Modem is a multi-port cable modem, then just configure the VPN router for a different IP address and connect to a different port (who is the ISP by the way and what brand of cable modem is it?)

With most charter customers, if the cable modem is a multi-port one, then they are for those with a block of static IP addresses. However, though I don't often go where Comcast is in this state, Comcast does deploy a cable modem with a built-in router (much like the AT&T 2-wire DSL modems).

If however, the customer has a simple, dynamic IP, and the cable modem is the kind where there is but one port, then simply putting the router you use for VOIP in the manner suggested above may work, but you will likely have headaches.

Is the router for their LAN so much better than the one you plan to use for VOIP that you can't simply run both off the VOIP router using QOS to give priority to the Voice packets?

Just wondering.