Lately there have been a lot of applications coming out that offer wireless back up of your contacts, which is great -- choice is awesome and everyone can have their own personal preference as to which is the "best". Aside from using SmrtGuard I did find iDrive lite to be a great free service to do back up your contacts and only your contacts. Online accounts are created from within the application itself which allows you to administer your contacts all from a nice PC-based user interface.
iDrive is a nice and lite application that does just as it says, backs up and allows you to restore your contacts whenever you choose to do so and stores it all within their secure servers. iDrive lite is available from BlackBerry App World now and is indeed worth checking out to see if it will fit your needs. Keep in mind, this application does contacts and that's all--no emails or anything else will be backed up.