Can I send an SMS message via one click or touch?
Can I have an icon or shortcut that would let me send an SMS message to a certain phone number with predefined text?
The Tasker app will let you do this (and much much more)
Once installed, add a "Task" widget to your homescreen, and have it run a "Send SMS" action. This lets you specify the target of the SMS, as well as the full body of the message.
5 years have past - I think perhaps the app OneClickSMS is a better fit for this task now (unfortunately it has been retired from Google Play but it's still available on mirrors with the original APK name com.utopia.oneclicksms).
It creates an icon on your home screen, and when you hit it, it sends an SMS with a single click. Very convenient.
A very light app (752k, no ads), with a sober theme, available on the Play Store : SMS Bot Widget