[psim1]

For three or four endpoints all within the home, you could do this with just ATAs and not even need a SIP server. Many ATAs have a configurable "dial plan" that will let you map a number to an IP address, thus giving you the ability to call the other terminals directly within the LAN.

[philips]

Do you have an ATA you like? They are all janky in different ways in my experience.

[psim1]

Janky is directly proportional to cost. Grandstream are the jankiest and least expensive. I like the Cisco 191; it is a fine unit but costs about $100-120.