To enable us to resolve this issue could you please turn-on trace logging.
To turn-on trace logging you need to do the following:-
1. Open the ActiveSMS Console
2. Goto the Transport page
3. Click Configure button for the active Transport
4. Select the 'Log Activity To File' option
5. Enter a valid Log Filename, e.g. C:\GSMModemLog.txt
Run a short test to re-create the problem. Once the test complete, please email the GSMModemLog.txt to mailto:support@intellisoftware.co.uk