Hmm... well, I don't know of anyway standards or commercial servers for doing this. If others know, please input!
Sending SMS would need a connection to a SMSC (interface is usually CIMD or SMPP) or WAP Push Proxy Gateway. Refer to the guides on creating applications for CIMD or WAP Push at www.Forum.Nokia.com
You'll need to be creative to figure out the solution since this is not a standard functionality.
What you could do is write an application that could be activated from your WML page... this application could then connect to a SMSC or WAP Push Proxy Gateway to send out an SMS message.
There are many web services which allow one to send an SMS. If one of those services offered a WML/WAP interface it would be no problem. If you were being creative, you could fairly easily write your own WML/WAP site that would essentially proxy the message over. In fact I think there are some perl libs that have code to interface with a large number of telcos' send-an-SMS websites. Maybe I should set up a WML version of that.