Cisco phone compatibility

I am looking to connect a CP-7942G or similar phone to an Asterisk server I will be setting up, but upon doing some research I found many places saying that some of these phones (specifically the ones with G in the number) supposedly require Cisco manager in some situations. When do these require this and how can I avoid potential incompatibilities?

I know this is really damn late but, the G stands for gigabit meaning its a newer model. Cisco phones never require call manager but its the correct way to use them. You can load SIP firmware onto the phones or alternatively you could install the chan_sccp module into freepbx or if its vanilla asterisk, the cisco asterisk patch. information on the topic can be found on https://usecallmanager.nz