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.
I just purchased VoIP service and added their phone port router to my existing network. Original router is wireless D-Link DI 624 802.11G router. The VoIP phone router (Linksys RT41P2-AT) is hooked to the cable modem, then to the the wireless router. The wireless D-Link router broadcasts wireless signal fine, but with it's own static IP range, which is different than the Linksys phone router. The wired/wireless pc's can't talk to each other. Also, the hardwire ports on the wireless won't work (just broadcasts) and I have tried an 8 port 3com hub from the phone router and that won't work either! I was so glad to save money with the VoIP but this has mucked up my network. I can't pass data between the wireless nodes and the wired. Any suggestions? P.S. I can ping host pc from wireless and connect with Terminal Services but this does not help me with data transfers. Please help! Thanks,
Linksys Phone router: 192.168.15.1 - All IP's are 15.xxx
D-Link 802.11G Wireless: 192.168.0.1 - All IP's are 0.xxx