@Frank Eory: I happen to catch some of the talk on M2M at the Sprint Developer's conference held at the beginning of Nov. I would say Sprint has done a better job of productizing M2M applications than all other mobile carriers combined!
Internet of Things (IoT) is one of the many incarnations for M2M; I strongly recommend engineers to visit Sprint's M2M Design center at Burlingame near SFO airport. They have some good use case demos and plenty of help to get started.
PS: Sprint didn't pay to me write this, I wish they had!! :-))
I would think for many things you'd get away with ZigBee or something similar, (maybe in 5GHz band), provided the machines are reasonably close together.
Obviously as range increases, cellular becomes the solution of choice, though it's rather fashion-driven, which can be a nuisance in M2M situations ... major change-outs as the technology heads towards obsolete. But so long as that's factored into the business, it should be manageable.
For very long range, you'll presumably be into satellite comms, though I guess things like marine oil rigs already have a suitable global infrastructure.
I have to say that strictly speaking, M2M mobile messaging is far from new .. I've was involved with it as an aside to mobile people messaging, H2M and M2H, between the early 70s and 2002, but the increasing availability of higher bandwidth infrastructure add much more 'power to the elbow' in the field.
It can indeed be a surprisingly interesting field.
I am very interested in developing M2M embedded computing applications.
Sprint may want Engineers, but their doesn't seem to be any JOBS listed for Engineers to develop M2M apps on their web site.
Something seems amiss ....