It is key to remember that the infrastructure or installation of servers is always the responsibility of the person who hires the Voice solution.
Depending on your case, to make the connection it is possible to use 
1. Own IP telephony platform: In this alternative, you must have a center that handles the SIP protocol, this being an essential requirement to establish communication (SIP Trunk) between the local IP telephony infrastructure and Voice.
In this connection method, it is essential to note that although Voice does not have restrictions for the number of simultaneous calls, this factor will directly depend on the bandwidth allocated for the use of the SIP connection and the methods used to establish the said connection.
Learn more about the SIP protocol
2. Virtual number If you do not have an IP exchange with SIP protocol support, you could access the Voice service with a virtual telephone number, geographically located in your area or Country. This option will have an associated cost, to be verified, depending on the country code where you are or where the number is required.
In the original version of Voice, you will manage it through an external IP telephony provider, an external company that offers DID (Direct Incoming Dialing) numbers, allowing you to receive calls anywhere, in this case, Voice being the destination that gets the call. Examples: DIDX, DIDWW.
For Voice 2.0 you will channel it directly with Aivo.
Key Data: If the connection is via Sip Trunk, it will be possible for the first contact to be the IVR and then go to Voice or for the first contact to be Voice directly. For the connection through a virtual number, the first contact will always be Voice.