With Voice on Mobile you can make outbound calls to your customers by using the VoIP dialer or your native phone dialer.

From the call details screen, you can click on the phone icon and choose "Call using... Housecall Pro Phone (VoIP)." This will use the HCP browser to dial that customer using the Voice feature on your main business line. You will also see this option on the customer profile, job, estimate, and lead details screens.