We have a client who would like to be notified when a new ActiveSync device is added. My thoughts are that this is not possible but I would like to confirm.
Well I'm not aware of a way to be directly notified if a new mobile device is connected, however you can use the Export-ActiveSyncLog powershell command to export activesync data to log files. There's a very good article on how to do so here.
Essentially this will take an IIS log file (or a set of log files using get-childItem) and parse them for ActiveSync data. It will produce a number of CSV files, the one you would be interested in is Users.csv which shows activity by users, including device type and ID.