setting up multicast routing for allworx phone system paging

i have a client inquiring about getting paging for their allworx system working between branches. As i expected, its using multicast for paging.

ill be honest, i just dont work with multicast routing much at all. In a situation like an allworx phone system, do i need to setup sparse or dense mode? im just not familiar enough with multicast needs and when to use one vs the other. since there are a number of phones at each location that would be listening, does this mean its a dense mode application?

im pretty sure the client just has one system at their main branch with remote phones, but its possible they have more than the one, i don't think they have a system at each location though.

if they are using carrier MPLS, or even metro E, does either throw any sort of monkey wrench in setup? or is the multicast router going to covert the traffic to unicast to the other routers before the multicast is sent out the local interface/vlan thats listening?