3rd-party applications cannot control audio routing or mix audio with an active voice call on S60 3rd Edition.
3rd-party applications on S60 3rd Edition have some limitations in their audio routing and playback capabilities.
1) VoIP applications: The voice will be directed only to the loudspeaker and not to the earpiece because all 3rd-party audio applications are treated as “Players/Recorders”.
2) 3rd-party applications cannot mix audio with an ongoing circuit-switched voice call. This is due to a hard-coded Vendor ID check in the mixing policy between 3rd-party "Players" and native telephony application.
3) Applications that try to play custom/video ring tones are not able to play the ring tone if the Nokia music player is playing music at the same time when there is an incoming call.
Audio preference and priority values sent by the 3rd-party application are ignored if the application does not have Symbian or Nokia Vendor ID. Typically developers’ VID is 0x00000000. Nokia’s VID is not available for 3rd parties.
Forum Nokia provides an Audio Proxy Server (APS) wrapper that can be used for creating audio streams with custom preference and priority values. APS is part of the Extensions plug-in package for S60 3rd Edition SDKs:
Extensions plug-in package for S60 3rd Edition SDK for Symbian OS, for C++, MR
Extensions plug-in package for S60 3rd Edition SDK for Symbian OS, for C++, Supporting Feature Pack 1
Note that S60 3rd Edition and S60 3rd Ed, FP1 devices require different versions of the APS server binaries.