Check out www.textmemos.com - a free, ad-free, web-based text messaging service where you can send yourself or others scheduled reminders (or other text messages) at specific dates and times.

You can text messages from your computer and even from your internet connected mobile device.

I've got the website bookmarked in Opera mobile browser on my old Ipaq hx2410 Pocket PC, and I can send myself text reminders to be delivered at just the right day and time.

You won't be charged anything when you use textmemos.com to send text messages, but, of course, the recipient of your message may still have to pay to receive them (depending on the plan they subscribe to through their mobile operator).