I am using a modern laptop or my iPhone to remote desktop into the old motherboard, connected to the RJ45 Ethernet and the RJ11 phone line. Can I use the RJ11 to make landline calls?
Check the specs of your motherboard. If it states the RJ11 port is Voice/Data/Fax, then at least it was possible on that motherboard. However, I haven't seen any software that allowed you to do it since the Windows 95 era.
I don't have a landline phone, but I have landline service to run my burglar alarm. I think I can use the port to use the computer as a landline phone/
RJ11 on laptop is used just for two things, fax and data, phone calls arent possible, well you could receive audio but nobody will hear you...this could be technicaly routed with software, and such software did exist, but it almost disapeared from the world, because we use VoIP for years now
Check the specs of your motherboard. If it states the RJ11 port is Voice/Data/Fax, then at least it was possible on that motherboard. However, I haven't seen any software that allowed you to do it since the Windows 95 era.