need to develop a voice conference software

we are looking for develop a PTT voice conference system with gps position of the hardware which can be able to received & transmit the voice over ( voip) mode in half duplex & duplex both & able to record the voice, the system need to work on lan ,wan/& internet envoironment ( without isp& with isp both) its need to configure with raspberry pi , the sdk & api documentation will be provide to the successful bidder ,