Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Caution - not compatible with RC 930 wireless modem system

I wanted to add an additional extension to my RC 930 wireless modem. This was the only RCA extension unit that I could find so I ordered it. I now know that the RCA wireless phone and modem systems are not compatible. RCA confirmed this over the phone and also said that the modem extensions are not sold separately.