There are two solution, which can be implemented. First is - DTMF Tone overlay and Second - DTMF Tone Masking. Both solutions are available as part of CVP/VVb 12.5
1. DTMF Tone Overlay - Its a built-in solution under CVP/VVB 12.5 and doesn't require any additional hardware or third-party solution. VVB has the capability to inject DTMF tones while customers could be punching in any PII information. These tones can programmed to be injected at random intervals so any third person listening would hear only random dtmf tones.
2. DTMF Tone Masking: This solution is end to end solution which requires a third party Hardware to mask dtmf tones. DTMF tones are masked on Voice Gateway itself and are never sent towards VVB. During CRM request, these tones are passed to VXML server via secure API request and no intermediate entities ever get to see dtmf tones.
Hope this clarifies support for DTMF tone masking on CVP/VVB 12.5.