ActiveSMS - SMS ActiveX
ActiveSMS is an ActiveX DLL that allows you to fully handle GSM, GPRS, HSCSD and UMTS terminals. Easily integrable into any application written in whichever language that supports ActiveX technology (Visual Basic, Visual C++, . NET, Borland Delphi, Power Builder, etc.. ... It supports serial connections , IrCOMM, IrDA, USB and Bluetooth and allows to communicate with the terminals both in PDU mode and in Text Mode. ... Reception and forwarding of binary messages (logos, melodies, EMS, WAP indications).
http://www.activesms.biz/download/ActiveSMSDemo.exe - 2Mb - Download - Screenshot

HS GSM SMS C Source Library
HS GSM SMS is a C source library that provides a PC-based user application with access to a mobile phone's Short Message Service (SMS) functionality, according to ETSI standards: GSM 07. 05 (ETS 300 585) - "Use of Data Terminal Equipment - Data Circuit terminating; Equipment (DTE - DCE)... Features: * Interface with mobile phone over COM ports COM1 - COM8 * Sending SMS messages to GSM network * Receiving incoming SMS indications from mobile phone * Reading received SMS messages from mobile phone * Deleting messages from mobile's phone memory * Decoding sender number and service center...
http://www.hillstone-software.com/hs_gsm_sms_demo.exe - 308Kb - Download - Screenshot

Wireless-DS for gsm modem
Wireless Dev Studio is an ActiveX DLL that allows you to fully handle GSM, GPRS, HSCSD and UMTS modems. Easily integrable into any application written in whichever language that supports ActiveX technology (Visual Basic, Visual C++, . NET, Borland Delphi, Power Builder, etc.. ... It supports serial connections , IrCOMM, IrDA, USB and Bluetooth and allows to communicate with the modems both in PDU mode and in Text Mode. ... GSM Data calls handling. ... Voice call handling (both incoming and outgoing).
http://www.wirelessdevstudio.com/download/WDSDemo.exe - 2Mb - Download - Screenshot