I dont get it. Why do I have to contact a web service for sending an SMS through a phone or modem that's directly connected to my computer? How does it help anyone?
It's a local application - it communicates via an HTTP endpoint, but it's a tiny little server that's cross-platform and whose only purpose in life is to make writing your killer SMS/geocoding/beer prices/petfinding application.
(disclaimer: I wrote it)
because carriers want more control over this process and make it harder to use by other means in order you to use your beloved phone, which completely bounded by your carrier, more.