I have 5 receivers in my household and so not all the rooms that they are in have phone jacks and if there are jacks they are not in a convenient place. I decided to go ahead and buy one 'Phonex" to see if it worked. It worked great without any problems, including the caller ID feature. However, the install guide cautions that you are not to plug the 'Phonex' into a surge protector, because it will not work.
I decided to go ahead and buy three more extension units. After browsing the 'web' I found that the extensions were about as much if not more than the initial transmitter receiver set. I went ahead and bought three more sets instead of the extensions themselves. I did this in case something should happen to one of the transmitters, then I had three spares.
When I got the three additional sets ($15 off Ebay w/$10 shipping for all three), I immediately installed them. When I went to program them, they would not work with the existing 'Phonex' transmitter that I had. I took one of the new receivers and replaced it with the original receiver and it worked fine. I wasn't sure what to think. Then I hooked up one of the new 'Phonex' transmitters and placed it the room where I had tried to get the new receiver to work and it worked great. What I found out was that those other three additional transmitters came in handy with all the rooms in my two-story house. Keep in mind when doing this, that you need to hook-up a phone line to each transmitter that you install. I could not get just one transmitter to work with all four receivers.
I was so glad I bought the 3 sets instead of just additional extensions.
FYI,
tvrocker2k5