Quick and Dirty SMS
How do you send a quick SMS message to someone without trying to figure out the email gateway for some random provider? There are a bunch of different solutions, but a one stop (and free) solution is GizmoSMS. They provide access without requiring accounts, but also have the ability to add your number to a blacklist if you are being annoyed through the service. Of course this appetizer is the bait to get your to upgrade to their premium service, but the free service works great in a pinch.
The user interface is really simple. Phone number, message and a captcha are all you need.
Even though the message is one-way, you get a confirmation that the message was transmitted to the network without error. Not bad for a free service.
The selection of countries to send free SMS messages to is very extensive.