Here’s a list of some of the available ‘PC to SMS’ services, courtesy of Russell Beattie. My own offerings:
Both Yahoo and ICQ chat offer some kind of SMS service, but I’ve found them to be somewhat unreliable. This is less to do with them and more to do with the end provider, but in the end if you don’t know your SMS has arrived, the service is pointless. The Asian experience, at least, has shown that free services don’t last, and people would rather pay a bit and know their SMSes have arrived, than try the lottery of a service that may or may not always work.
I’ve noticed Americans getting into SMS in the past couple of months, presumably because of improved services over there, which is great. Hopefully this will lead to an improvement in inter-carrier operability. Europe and Asia have long had these services — and the ability to send SMS between continents — so perhaps this is the start of something big.