1. Use Regedit to edit the Windows registry on the Swyx Server
2. Navigate to HKEY_LOCAL_MACHINE > SOFTWARE > Wow6432Node > Swyx > LinkMgr > CurrentVersion > Options
3. Right-Click and create a new ‘Key’ registry entry named:- GeneralLinkConfiguration
4. Right-Click ‘GeneralLinkConfiguration’ and select New > DWORD (32-Bit) Value. Name the new DWORD entry DTMFGapDuration
5. Set the DTMFGapDuration to 100
6. Right-Click ‘GeneralLinkConfiguration’ and select New > DWORD (32-Bit) Value. Name the new DWORD entry DTMFToneDuration
7. Set the DTMFGapDuration to 400
8. Right-Click ‘GeneralLinkConfiguration’ and select New > DWORD (32-Bit) Value. Name the new DWORD entry DTMFVolume
9. Set the DTMFGapDuration to 200
For Swyx 2015 please see latest blog: http://www.knowall.net/swyx/how-to-increase-dtmf-signal-strength-in-swyx-2015/