Wireless-DS for gsm modem 

Wireless Dev Studio is an ActiveX DLL that allows you to send and receive SMS (also binary, flash, Unicode (UCS2) and ultiple SMS) through GSM modems. It handles voice and GSM data calls and the phonebooks of both SIM and terminal.
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SMSLibX 

ActiveX component (DLL) for sending and receiving SMS from PC using a GSM modem. Very simple usage in Visual Basic, ASP, C#, C++, Access(VBA) etc. Features: sending, receiving, status reports, long sms, logo/ringtones/ems, phonebook. Help online.
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