Michael Robertson, the founder of MP3.com, is now involved in all sorts of other online pursuits. One of them is with VOIP. He has grouped several services under the Gizmo Project name, and the latest one is GizmoSMS.
[GizmoSMS is] a web site that lets you send SMS messages to any mobile phone directly from your PC. It’s fast and easy and best of all it’s free.
I tried it the day it was launched, and it took 2 hours to get to me. I tried it just now, and it took about 30 seconds to get to me. If you are looking for a quick and easy way to send a text message to a cell phone, GizmoSMS is a good place to start.