[techsupporter]

Short code delivery doesn’t depend on whether a number is assigned to a mobile endpoint, only if the owning carrier has an agreement to exchange messages with the short code provider. Google Voice can handle most short codes, as could Bandwidth.com’s old “demo” retail service, ring.to. For example, send the word “help” to 468311, the short code message service a lot of public agencies use for alerts, from a Google Voice number and you’ll get a response.

Any number can be provisioned at an SMSC, even toll-free numbers these days. But mobile providers—and the associated short code entities—are loathe to peer with many VoIP carriers. Partially for competitive reasons, partially because many short codes are premium billing numbers.

You’re right about non-mobile numbers being second class, but that’s largely because companies filter them out because “fraud,” which is also suspicious reasoning. I can get a hundred “mobile” numbers within a few minutes, rather inexpensively.