Modern 3G IP Radio PTT server

I would like to experiment to have and test to learn more about Asterix.

The modern 3G IP Two way radios using POC /PTT over cellular.

How does one start making and more importantly learning the architecture to run such a POC /PTT server.
Ultimately I would also like

  1. Server to interface to an analogue Base radio .
  2. Accessible from a SIP connection
  3. Accessible from a remote PC using VOIP or similar software.

The radios I am talking about are the iWalkie , F25 , F22 and many more now available .

Thanks in advance