There are already networks dropping support for 2G and I assume 3G will follow. These type of devices need to last at least 10 years if not more. The mobile networks don't work on that type of time frame. A lot of the modules out there already won't work on most networks because they don't support 2G. GPRS doesn't help either as that is being dropped too.
I envision devices that these would be put in to actually use well established low power wireless protocols. These devices would then talk to a router that could be directly connected to the internet or have a module like this. But this type of setup doesn't require an extremely small module. Especially when you take the power requirements in consideration. If I have a huge battery, do I really care about the size of the wireless module? Or... if it is plugged into mains and mounted somewhere on the side of my house do I really care about size?
I also don't think the cost of the connection would be an issue. These devices would have different terms to connect to the wireless networks and most likely be under a blanket contract that is resold by the supplier of the product. Think OnStar.
But to expand on the router concept... Predictions say we will have several connected devices in our homes. Everything from our blenders to our stoves, dishwashers, laundry, etc. There is no reason for these all to have a device that directly connects to a national wireless network. It makes more sense to have a household or neighborhood router that relays these signals. It will be cheaper to upgrade and will cause less congestion on the cell phone network. Comcast is already installing public hotspots in everyone's home. I'm sure similar plans are in place for other providers globally. These routers could have other wireless routing technologies installed to allow lower power devices to connect to them. At a minimum if you own a IoT device you can just get a router that plugs into your internet connection.
This doesn't necessarily cover the idea of the electric company wanting wireless connectivity to your meter. You may not have a router for them to connect to. Then they can just install something on the electric pole. In quantity I don't see a device costing more the $10 - $20. They could be on every pole and probably already are.
Small devices don't need to connect to cell phone networks. Add a relay and be done with it.