Hi Michael
I have been in a similar situation before of having Paging to traverse over the WAN IP MPLS network with SingleWire Paging system. If we are talking about Audio paging, it is built on the IP multicast networking and thus to extend this service to remote offices connected through IP MPLS network, the Service provider should enable IP multicast over its VRFs for you. In my case it was not feasible by the Service provider(s). SingleWire introduced a solution of a Paging Gateway that is integrated with the paging server and it is located at the remote office. The Paging server sends the target audio mulitcast as a unicast session to the paging gateway in the remote office and then the paging gateway sends on the LAN as a multicast .
I am not sure if IPcelerate has a similar solution, but it is worth asking and validating.
Hope that helps
MonieM