SIP Audio converter (convert any audio to sip protocol)

We want a voip professional/developper/engineer to create a code to be able to convert audio to sip protocol and from sip protocol to audio. The code can be uploaded to a raspberry pi/arduino to be able to connect a microphone and headphones in order to exchange sip & audio.
Creating a project similar to this device (https://www.cohesiveglobal.com/marketing-materials/2n/datasheet/sip-audio-systems/sip_audio_converter.pdf)

Pls read well the project and check the link, and pls bid if you can make something similar