I agree with what Kenn commented on. We already have the NG lines infrastructure and would just need to have pumping stations added. Seems to be the easiest way to move forward.
It's a catch-22! In order to convince people to spend the money to convert, they'll need a place to fuel up. The market economy won't invenst in fueling stations unless there is a demand. As much as I despise government involvement, there would have to be some type of tax break or credit to gas stations to add NG pumps (something similar to the Florida program promoting the now defunct E85 "solution.").
Since the distribution network already exists it would be simple to just have your own home based refueling station. If you were traveling you could go to a commercial station which would be easy to set up wherever there is access to municipal natural gas. Here is a story on home based CNG fueling stations from Green Car Congress:
If you could create a home based solution and use the existing network of Natural Gas to impliment stations throughout the USA. In my opinion that would be the fastest way to get this done.
When automobile were new and people needed gas along the infant national highway system, people were offer incentives to offer a value proposition to drivers. In return for services, (like pumping the gas,checking the fluid levels and tire air pressure), motorist were willing to pay for the fuel.
This may be oversimplification, but for a generation that has known nothing but self-service, its a radical concept. The auto industry prefers to sell us electric vehicles, not natural gas \electric hybrids, but almost anything other that natural gas including ethanol, alcohol, and hydrogen. Those may be the ultimate fuels, but they are impractical for the immediate future (like the next 15 to 25 years.
Natural gas is already in many of our neighborhoods as there are 1.5 million miles of gas pipelines across the nation serving residential and commercial buildings. Tapping into the distribution network to distribute this fuel is a relative no brainer that requires a lot fewer tankers rolling down the road. So, the real trick is who will operate these refueling stations and what incentives will be offered to the operators?
It doesn't take brillance to imagine the conversions at typical petro-product dispensers. Its just another truck pulling up, only instead of transferring the fuel from delivery vehicle to below ground storage, the very tank that holds the liquified gas is left behind. A system designed to further lower the temperature of the gas and compress it for retail dispensing is installed to fill the vehicles much in the same way that space ships are fueled. Only trained people are allowed to 'service' customers refueling needs and all conversions are required to have a quickly replaceable tank refueling system.
This drastically changes the fuel dispensing and distribution industry, but serves a purpose in the name of safety and ecological responsibility. The expense of the refueling systems are offset by the hybrid nature of the vehicles. A lot less fuel and a much smaller tank is required for a hybrid vehicle that gets 40 - 50 MPG on natural gas at 35 to 45 MPH and 650 to 350 MPC (Miles per Charge) at 46 to 85 MPH with four adult passengers. To get the optimal performance at this load the natural gas requirements is about 3 to 5 gallons. About the size of a bar-be-que grill canister. some vehicles would have two, others just one.