If you use a Sipura/Linksys, these are the settings that work for me:
http://forum.voxilla.com/general-voi...dtmf#post92173
On any SIP device, you'll have three or more choices for DTMF tones: auto, inband, AVT (rfc), and INFO. What you'll have to do is try different ones, save your settings, and then make your phone calls and see if the touch tones are recognized properly on any of them.