Broadband is the easiest way to bring VoIP to the edge. But it is not the only way. Don’t forget those huge numbers of Class 5 switches installed around the world. Carriers are not going to simply sell them as scrap. Before hosted telephony in form of VoIP over broadband (or VoBB) became hip around 2002, carriers were engaged in long term Class 5 replacement planning.
Class 5 switch replacement might seem an archaic way to transform your network, but hosted VoBB could also prove to be just a diversion for a while. Carriers will eventually have to migrate their Class 5 switch infrastructure over to IP. Hosted VoBB could be one of the iterations a nextgen Class 5 switch supports. Either that will happen or we could have a flat ‘Classless’ network where physical separation of access and trunking features does not make sense. In the latter scenario it is logical to assume to intelligence will migrate from the core to the edge.
If neither of those scenarios develops, then some compromise between the two will take place i.e. varied types of access networks (DSL, PSTN, GSM) will be supported by an intelligent IP core whereby the carrier remains relevant retaining some intelligence in the core. This is the IMS scenario.
Two years back the incumbent service provider strategy was to let VoBB grow in parallel to PSTN and through some multi-service access technology bridge the two networks (broadband and narrowband) together sometime in the future. My understanding is that the thinking has changed somewhat. These incumbents have tested VoBB and are now back to the square one. The Class 5 replacement debates are very much in.
There are three broad ways of doing Class 5 VoIP: (1) hosted VoBB, (2) take TDM handoffs from customer, convert to IP in the CO, and dump traffic into IP cloud via BLC/DLC, and the third way is (3) the BT 21CN type deployment where you deploy VoIP access gateways and either packetise voice in the CO or put access gateway card in the street cabinets and packetise right there. Methods 2 and 3 include option 1 provided customer has access to broadband.