SMS scheduler seems to be widely available for Palm device, but not found any for BlackBerry's. Hopefully someone else will be along shortly that has a solution...
I take it email is not an option? If yes, and you're on Exchange, you could set something from within Outlook. Since Outlook has the ability to send an email at a designated time...
Hi. I just posted this as a reply on another forum, but I guess I'll post it here too just in case people are interested.
There is a website called www dot ohdontforget dot com which I think is kinda what you are looking for. The only downside is that the SMS is sent from '[email protected]' instead of your number, but I guess you could sign the text so the recipient knows you're sending it. You input any mobile number, when you want the text to send, and what you want the text to say. I use it to send myself reminders all the time, and I see no reason why you couldn't use the site to send others messages. The interface is simple - you just type in "tomorrow, 6pm" or "now" or something like that for when you want the text sent. As I said, it's a very useful site. Hope this helps.