Not sure how this would this work. The MNO would have to ask the customer where they live? Or where they might use the service?
BTW accountants don't approve expense - budget holders do.
The check is done at their home address.
I understand the point that it is a mobile service so maybe not as simple as I thought, but there needs to be something to provide an incentive for them to build the transmitters.
Roaming is probably what the networks would love, especially those who have under invested such as O2 and three.
Budget holders are basically accountants, like how most CEO's tend to be qualified accountants.
Another idea is the phone is made to log the amount of time it has no signal (already does this), then based on % of time with no signal, the monthly fee is reduced accordingly, so e.g. 15 days of month no signal then say 50% reduction in cost.