When making calls from a DPH-125MS phone with firmware v1.14.25 through ITSP Optimum Voice for Business (Microsoft Certified) to numbers with IVR systems (e.g. - 800-555-1212) the call gets no-way audio.
When the call is made from a DPH-125MS phone with firmware v1.14.19 connected to the same system the call completes and works successfully.
The ITSP has identified that the v1.14.25 phones stops sending RTP when it receives ia 2nd SIP message with SDP attributes in it (i.e. the 183 and then 200 OK).
Is this a known bug? Is there a new version of firmware to fix it? How can I downgrade from v1.14.25 to v1.14.19 so I can get the phone working again?