Each unit will have an RJ11 connection jack within the living room. This jack is able to handle the Intercom system, or provide for a VOIP/SIP phone service. Since this is in reality an obsolete jack, there will only be one per unit. For those that needs a phone in multiple rooms should consider a cordless phone system.
To connect with other SIP providers, the tenant will log into the phone system, and enter their credentials. When that account is rung, it will send the call directly to the RJ11 jack. Those that won’t use this jack for SIP will still need a telephone plugged in for the intercom unless they are using a SIP client on their phone.