We don't recommend it but it's possible, although you would need additional equipment — a splitter — to do so.
A splitter basically splits your phone line into 2 or more lines. It looks something like this:
Our Analog Telephone Adaptor (ATA or voice adaptor) device that is required for Home Voice to work comes with 1 telephone port.
If you wish to have 2 phones to share the same line, you can do so by putting a small 2:1 RJ11 splitter in front of the ATA to connect multiple telephones. These splitters can be purchased from an electronic hardware store.
If you already have a phone wiring set up in your home, with multiple phones already connected, there should be no problems at all. Instead of where all your phones used to receive their signals from (e.g. the phone port in the wall), insert the common phone plug into the ATA.
Do Note: In some rare cases, when cables are a bit old or degraded, or when some specific phone models are connected together, there can be a mismatch between the multiple phones and the ATA, causing problems like a lot of noise on the line. Most of the time there should be no issues though!