Some providers offer a "data only" sim card. Do these types of sim cards have a phone number assigned to them? If yes, what happens if a dial out is attempted of if there's an incoming call?
A number has to be assigned so that the (rather old) system can recognise the SIM.
Just because it has a number though doesn't mean that any calls can be made or received and will already have been disabled by the network.
The provider can add services as wanted/needed though: SMS can be useful for managing routers.
Usually, they have. Usually, "data-only SIM" only have a special tariff plan with cheap data service rates, and is an ordinary SIM from all other points of view.
Finally, it fully depends on cellular provider - it can allow voice services, or it can prohibit them.
So, the only way to get a correct answer is to try.
Yes, they do have number, perhaps, special number, taken from a specialized pool of numbers, allocated for certain purposes, such as assigning tailored tariff plan to them.
You might hear of "Numberless" sim cards in some parts of the world, however, these sim cards aren't entirely numberless. You'll need a number to actually use it.