This issue has been posted a bunch of times before, but always in relation to DAHDI/PRI/BRI. My client is all VOIP. We have no analog connectivity.
Occasionally while on a call, a client on our end will hear seemingly random dialing tones. It was only reported by a single user so I spent a month or so tracing his calls, but recently found out that others have had the same issue.
One client called me to report this was occurring, and during the call it happened to me as well. This was a direct call, so no trunk inbetween. Just SIP>SIP, phone>PBX>phone.
What might cause this?