WebSMS is a nice alternative to send SMS from your carrier's web site. It automates all the boring stuff. It's easy as the cell phone: compose, click, sent!
It gives you one-click access to your mobile contacts from the Address Book. Use a different phone color for each one of your frequent contacts. It even supports CAPTCHA's.
Released under an open source license, it can be extended to support new carriers writing a plugin. A thoroughly commented template lets you create your own plugin in a minute.
WebSMS is neither affiliated to nor endorsed by the supported carriers.