Hi, I'm a VoIP specialist with over 10 years of experience working on the TS department of a US VoIP company; I can install, troubleshoot and customize many VoIP devices including: softphones, ATA's, IP-phones and PBX systems like Asterisk/FreePBX. I read your project description and I can help you troubleshoot and resolve your DTMF issue. You may contact me through chat at any time to discuss your project further and get started. Thank you.