If your Motorola phone has "limited" contact support (see below), the "Only synchronize contacts with phone numbers" option in iSync could cause email addresses to be removed from your phone (but remain in Address Book), if you entered the addresses on the phone itself. This can happen if you've selected the "Synchronize email addresses" option, which is off by default.
This applies to all versions of iSync, including versions 1.5 and 2.0.
For example, if you enter a name with an email address on your phone and then sync with this option off, iSync will sync the name and email address on the phone with Mac OS X's Address Book. But if you turn this option on and then sync again, the contact's email address will be removed from your phone.
As a workaround, use Address Book to enter email addresses for your contacts instead of entering them on your phone.
By "limited," we're referring to phones that can only store names, text email addresses, and phone and fax numbers for each contact. If your phone can also store other kinds of information for each contact, such as notes and URLs, it's probably not "limited," and this issue shouldn't affect you. For example, Symbian OS-based phones are not "limited."
Important: Information about products not manufactured by Apple is provided for information purposes only, and does not constitute Apple's recommendation or endorsement. Please contact the vendor for additional information.