@Leafle
Ok, visual is better
.
So I am not sure which interface the VoIP client is working on - the LAN or WAN on the Linksys. So why don't we switch them the other way around and do it the easier way. To do that:
1. On that config page on the Linksys leave the Internet connection as PPPoE and enter your valid Teksavvy login credentials. Fill in some hostname - "rtp300" could be proper. Leave the Router IP as is - 192.168.0.1. This means your internal (LAN) subnet is 192.168.0.* and all IPs will be in that subnet. We will need those in the D-Link. Enable the DHCP server and save the config.
2. Connect the Linksys to the modem. That is WAN of Linksys to the modem.
3. Connect your laptop/desktop to the LAN of the Linksys and make sure you get Internet connection as well as the web interface at 192.168.0.1. At this point the VoIP should work as well.
4. Disconnect your laptop/pc from the Linksys and connect it to a LAN port of the D-Link. Do not connect anything else to the D-Link for now.
5. Get to the web interface of the D-Link and disable its Internet connection. Disable its DHCP server. Enable its wireless and set it up as you wish. Now set its LAN address to be 192.168.0.2 (this is within 192.168.0.*). If there are fields for Gateway and/or DNS input 192.168.0.1. Netmask is 255.255.255.0. Save the config and reboot the D-Link if needed. Effectively we have configured the D-Link to act as an Access Point only.
6. Connect the D-Link to the Linksys via LAN. That is a cable from a LAN port of the D-Link to a LAN port of the Linksys. Do not use the WAN port of the D-Link.
Now the Linksys is your router and VoIP box, and the D-Link is your wireless access point. You would connect all wired computers to the LAN ports of the Linksys and/or LAN ports of the D-Link (the LAN ports of the D-Link act as a switch now).
If you have problems with the configuration of the D-Link - provide the needed snapshots as you did for the Linksys (with available options for the dropdown fields) and I will help you.