There are portal services who for a fee will send out SMS's. Although I'm not sure how they handle number portability. Most carriers have a special email address you can SMS through, but there's no standard to the format, and you'd have to know which carrier a given person was currently signed on with to build the address.
Just as well. It probably limits SMS spam. And SMS spam, like telemarketing, has an infuriating level of intrusiveness. Only worse, since if it every really caught on, people's phones would be lighting up like pinball machines until they finally threw the whole
unit away in disgust.