There's a new push purveyor on the mobile scene, come to show the competition what's what -- despite being completely dependent on that competition, at least for the moment. Hot on the heels of RIM adding a push API, Google is enabling some BlackBerry users to get their Gmail and Google Calendar goodies shoved straight to their handsets. However, there are a number of shortcomings here that make this addition somewhat limited in usefulness. For one thing users have to be connecting to BlackBerry Enterprise Server instances, and furthermore those instances have to be backed by Microsoft Exchange. Additionally, only 250 users per Enterprise Server instance can get their mobile Gmail on, changes made to appointments on a handsets cannot be pushed back to Google Calendar, and to top it all off searching for Gmail messages still requires a separate app. Updates and improvements are coming, but until then it's caveat emailor.