sbiddle:
You're still failing to acknowledge the fact existing mobile technologies are focussed around providing legacy switched circuit voice services. They are not primararily intended for delivering IP or IMS services and simply don't have the ability or capacity for this.
Simplistically, a mobile call/text/data uses the land based lines.
Mobile phone to cell tower to land cable network to cell tower to receiver mobile phone.
Telco's need revenue to pay for access to the network, R+M and expansion of cell towers, CSR support, admin, power, Land and buildings for staff, etc, etc, etc. You cannot say, well I pay $x for landline, broadband, mobile call/text/data plan. I will replace that with a naked DSL and cheaper mobile data only and save 70% on costs.
Unless your happy wth zero expansion of cell towers, and vastly reduced Telco staffing, and a base, minimal support to the point of, "your line is active from here"