Hello, Pix! As I understand TFO is protocol between two transcoders, but not between trau and MS. My knowledges in this area are very vague and I need learning:). Moreover we are saying about TFO as Tandem Free Operation (inband signalling), but not about TFO as Transcoder Free Operation (outband signalling), isn’t it? Collision between trau signalling or even radio-encoded speech on PCM and DTMF may occur when MSC interworking equipment generates DTMF (from mobile) simultanuously with TRAU signalling. There is no standard way to deliver DTMF from network to mobile and the gsm codec in trau heavily distorts DTMF tones when they come from network in speech channel.