Defining two routers on same LAN and 2 WANs

Hi,

I am trying to add a WAN connection to a customer VoIP deployment so Voice traffic could go through a separate WAN connection (will not go on the existing WAN connection where data is carried) instead of PSTN line. Does anyone know how to configure the two routers that phones will pass through one where SIP trunk is defined and all other traffic will go over the data WAN? Thanks