Hi, So on a customer site I have a UK BT PSTN line with a linksys SPA 3102 on it acting as a gateway to a 3CX PBX. Nothing new here - do it all the time. However I am having issues with DTMF. If I call the PSTN number using my mobile, my home landline, from a work handset on our ISDN - DTMF works as you'd expect within the digital receptionists - no problems there at all. But.. If I call the PSTN number using a handset that goes out over OUR voip unlimited SIP trunk, DTMF detection on the customer site is intermittent at best and often doesn't work at all. There have been reports to the Customer from their customers that DTMF doesn't always work too, so its likely not just my handset/sip trunk provider combination here that suffers from the DTMF issue. Any ideas? Any one seen this before?