You will need to find out how much of the CRM functionality they need/use: if they only use the phone bit, then yes, outlook/exchange can mostly replace it, provided their handset or VOIP service/server doesn't mind talking to windows desktops/outlook.
There's also plenty of open & free services and server-apps-with-client out there to replace any commercial CRM or groupware service/server.
I'm sure Google apps is no exception, so help them get started/playing with it: you will get to know each other better and they will think of you as being a more valuable IT service guy.