I would recommend using an ActiveX control. Different carriers use different methods to send/receive SMS messages.
Another method that we use is to send an email to the carrier/phone
example : 1234567890@mobile.att.net would send a message to the person.
Good luck
Mike
Mike Crabtree - Lead Developer
Destek of Nevada, Inc. / Digital Telemetry Systems, Inc.
(866) 964-6948 / (760) 247-9512