In recent years, some have moved to the use of ATM service MUXes. Now, one can envision IP-based Integrated Access Devices where the voice is packetized over the WAN link, sharing bandwidth with all the data and video packets. Combine that with new WAN access methods such as xDSL and you can radically reduce the cost of WAN access bandwidth. The WAN access bandwidth can then be carefully managed to implement various policies of usage. You don't have to inflexibly provision some DS0s for voice and some for data.
All bandwidth is potentially available for all services.
Alternatively, the voice could be compressed more so that it takes up less bandwidth, at the trade-off of slightly less quality for a short period of time. The internet is free, but performance varies. We already use it extensively for one called e-mail. The performance requirements for FAX are essentially the same as e-mail. You are already used to some degradation of quality when talking overseas.