Cell2Jack can be sharing by two cellphones.
Your home phone will ring if there is an incoming call for one of the cell phones.

To setup the second cellphone, press #*# (or 0000) from your home phone to enter pairing mode
In your second cellphone's Bluetooth setting, click search to find cell2jack then click to connect.

Note:
Some cellphone may have interference to other cellphone's Bluetooth when both connect to 
same device (cell2jack) and causes some stability issue.