I recently discovered that there is an issue with the Skype for Business (build 35.8.253.228. There is an issue with this build that does not send DTMF over the RTP stream even though the RDP information is there. This impacts the ability of the end user to interact with auto attendants or account codes for LD carriers. Yealink has acknowledged that this is an issue and is working on a fix. BTW, their new ticketing system works pretty good.