I'm not sure about the VoIP equipment, but I think I would put the VoIp at the end of the line (cable modem, then Wireless router, then VoIP router).

Secondly, you need to match the subnet ID's on both routers, all 192.168.15.xxx OR 192.168.0.xxx. If you have both 15's and 0's, there isn' any way PC's on separate routers to have two way sharing with you setup. Example: the VoIP may 'see' the wirelss PC's, but not the other way.

Check out my answer for a similar problem at http://home.comcast.net/~larbel1/ . You may be able to come up with the solution for your problem. The CNET forms wouldn't format my simple text drawing correctly, so I did it on my web page. It will be up for some time.

Good luck.