smssend is a utility providing a command line interface to the GSM
Short Message Service (SMS) via internet gateways. It requires an
active internet connection (HTTP proxy is suitable) and may require a
registration for such gateways. The program is quite configurable for
other gateways than provided, examples are included.

Keep in mind that these internet to SMS gateways may not tolerate and
may even forbid their use via scripts.