Raspberry Pi SIP VoIP Phone Development

I'm looking for a experience engeneer to develop a VoIP phone using a Raspberry Pi. The primary purpose of this phone will be for business use. Key Features: - This VoIP phone should utilize the SIP protocol. - It should come with a basic graphic interface. - IP use of ethernet interface is necessary. - The phone should be able to make direct calls to pre-defined numbers - Low power consumption Ideal Skills and Experience: - Extensive experience with Raspberry Pi. - Proficiency in SIP protocol. - Prior work in VoIP phone development. - Ability to create user-friendly interfaces. - Knowledge of ethernet integration. - Experience with business-grade telecommunication solutions.