Multiple WAN, Voice QOS on Cisco 881

Hi all!

This is my first post, and your truly have learned everything in here...

I've got a Cisco 881 Router with 12.4 IOS.
I have two WAN: PPPoE (Telefonica Speedy) and a WiMAX leased line (2mbps 1:1, Ethernet) with a /29 IP Pool.

I have a small call center and I would like to do the following:

First, segment my network. I would like to use the Router and my L2+ Switches to do that. Is that possible?
Secondly, All voice related traffic (that's a SIP Trunk) must go through the WiMAx Line, but use the PPPoE as a backup in case WiMax Fails.
Also, All other traffic must go through PPPoE Interface.

I've noticed this router do have 5 Ethernet ports, one named WAN and the other is a managed Switch. I have tried the config but no joy.

Can you help me????

Thanks a lot!

can u explain brief wat u want to do ? backup for what . wimax used for voip or internet . what is other technology ur using like dsl or adsl ?

multiple wan is possible . just need to create subinterface in interface 4 .( 1 wimax only u can provide internet and voip also )......based on my knoweldege .