Just yesterday <http://www.theregister.co.uk/2014/07/23/telstra_to_kill_2g_network_by_end_of_2016/> Telstra wanted to turn off 2G in a couple of years because of disuse.
I'm thinking with OnePhone, they're trying to repurpose the network to justify the bandwidth use fees.
Much like the carriers in Australia converted to CDMA the moment the old analogue phone system was dismantled. They had already paid for the bandwidth, and CDMA "coincedently" used exactly the same channel slots. Later on, once it was clear GSM use had spread and was going to win over, CDMA became the unwanted bastard child of mobile phones. They never got any special deals, and CDMA<>GSM call deals were notibly absent even though there were carrier to carrier call deals present all over the place. Lots of the advertised deals had a notable asterisk that said "CDMA phones excepted".
Of course, I'm making the assumption 2G and 3G live on separate bands.