VoIP with Dual WAN

[bobm]

I'm trying to help someone set up a new NW with a 60C, and not sure how to approach this.  They have dual ISPs that they want to load balance, but will be using hosted VoIP from one of the providers, so need to make sure all the voice traffic goes over that one link. 

Is this best handled by Policy Routing? Traffic Shaping? Something else?  I've looked around and found some info on the finer points of VoIP configs, but not the big picture approach of how to set this up.

Also, I'm assuming that if WAN1 (data and voice link) goes down, the traffic would fail over to WAN2 (usually data only) until WAN1 comes back up.

Any help is much appreciated. Thanks.