There are a few scripts out there. Try checking out chickensms.com. I know the owner pretty well. Good guy.
gmail now lets you send sms through your account - currently only available in the US but soon in the UK and im sure someone will develop an external API to facilitate this on a website.
I'm looking forward to it going further abroad than that... happy to pay even. Skype is good too but I can never remember my password when I'm away from my regular pc. In the meantime neither skype nor gmail are practical for the OP - so it's back to Clickatell or Chicken SMS
You need a script to use that function such as this http://www.findmysoft.com/scripts/SMS-Text-Msg-script-with-auto-network-locator-download.html