There is no J2ME involved in your case! J2ME is a client side technology for creating applications that reside on mobiles. But, as you have stated you want to send SMS from servlet(s). You are better off with server technology as Servlets.
I haven't created such service but let me give you few pointers:
1. You require an SMS Gateway, which acts as an interface between the "Internet-world" and the "Mobile-netword".
2. Try to findout the providers for such service.
3. Find out how the messages should be forwarded to use their service?
4. I guess they will provide their own API classes to use the same.
Hope more information will be posted by others....
For low volumes, there are email to SMS gateways for nearly all the carriers (in the US). You can just send an email to an appropriate address. It varies by carrier. You just address it to something like