At the risk of self promotion, the company I work for offers an SMS Gateway (deployed on Jboss) and we provide different integration APIs. Send me a private mail and I can give you with more information.
it depends on the SMS Gateway, we integrate such system via a JCA implementation because the necessity of XA transactions. The SMS should not be sent in case of a failure.
Also I would recommend to use JBoss 5.1 because the version will have less bugs.