When a new contact is created either in a Google Apps account or on a BlackBerry device, the minimum required fields are either First, Last or Company names. These fields are required to be populated in order to be able to save the contact in your contact list or address book. These fields are also the default fields that are synchronized in between the BlackBerry - Google Contacts list. The rest of the fields (i.e. title, job title, email, phone numbers, address, etc) will be synchronized both ways only if any of them are populated.
On an iOS device, First, Last or Company fields are the required and default fields that are synchronized when a new contact is created either in a Google Apps account or on an iOS device.
All of the predefined fields in Google Apps sync except for custom fields - these are the fields that a user can create from scratch for any profile in Google Apps. If custom fields are created and populated with information in Google, that information can be seen only in Google Apps and will not be synchronized with an iOS or a Blackberry mobile device.