Typically 3G modem can send and receive SMS at the same time when network connection is active. It depends on the modem if it (and it's driver) provides an interface which can be used by SMSTools.
For example Huawei E1552 on Windows 7:
- It provides the modem port ( COM8 ), Application Interface ( COM7 ) and PC UI Interface ( COM6 ).
- If 3G network connection is created by the Windows networking, PC UI Interface is free and can be used by the SMSTools. Sending and receiving SMS works fine, and does not break 3G connection.
- If 3G network connection is created by the Mobile Partner application, this application reserves the PC UI Interface and SMSTools cannot use it at the same time.
If a modem provides only single port, it typically blocks the SMS usage. In this case some multiplexer might be useable, but it depends on the modem and operating system. See this posting, there was gsmmux
used with GPRS modem: [solved] SMS usage at the same time when the GPRS connection is active (post #6)