Sometimes VOIP providers don't send the DID number properly, and your system receives the 's' instead of the DID number, but the system can transfer this to a real extension like this.
Login to the system shell as a root user
Edit trunks-in.conf file
nano /opt/pbxware/pw/etc/asterisk/trunks-in.conf
Find and copy your trunk settings, for example:
[TRUNK_NAME]
exten => _X.,1,Agi(agi://127.0.0.1)
exten => _X.,2,Hangup()
exten => s,1,Agi(agi://127.0.0.1)
exten => s,2,Hangup()
exten => t,1,Hangup()
Press 'CTRL + X' to exit the editor
Edit 'extensions.conf' file
nano /opt/pbxware/pw/etc/asterisk/extensions.conf
Search for #include trunks-in.conf line and paste copied content right above. Modify it so it looks like this
[TRUNK_NAME]
exten => _X.,1,Agi(agi://127.0.0.1)
exten => _X.,2,Hangup()
exten => s,1,Goto(default, 1000, 1)
exten => t,1,Hangup()
Press 'CTRL + O', 'Enter' to save the file.
Press 'CTRL + X' to exit the editor.
Reload Asterisk configuration:
/opt/pbxware/sh/asterisk -rx 'reload'
Above configuration should send all calls with s instead or a real DID number to extension 1000 on the system.