You don't have to buy a Linx or their phones. I use the phone I had and to get extensions I bought a three phone set from Home Depot
I used a double connection at the telo for the two lines. one for the phone I had and one for the three phone set. This requires some phone line along the baseboard so you can place the phones where you like. My tele is in the bedroom where I have two phones. One of the extensions is in the kitchen and the other is in my office.
I've had Ooma for probably eight or ten years. I love it.