Question : Cisco 2801 VoIP configuration

Could someone, please help me and post the example of the configuration for the VoIP services on the cisco 2801 router.
I have a connection to the Internet by DSL designated for VoIP comunication and on the other site I have to connect to the PBX Simens Hicom 350E. The router is connecter to the PBX by two BRA links.
All calls from inside should be redirect to the VoIP number. All calls from the ouTside should be redirect to the internal voice numbers from 2000 to 3999. The incoming calls will be answered by IVR with simple communicate and then pass to the PBX.

Answer : Cisco 2801 VoIP configuration

I was considering the Qsig usage.
I have not yet configured the router? Honestly I am quite confused from what point I should start.