Originally Posted by Thatzmister2u
It's all or nothing with Blackberry. Menu>options>Password>enable. After 10 wrong tries it wipes the whole device. You can't protect just certain applications playa.
Maybe you could set all of your contacts in your address book under the Personal Category and then set the ones you're trying to hide under the Business Category. Then set the filter to only show personal contacts.
That may or may not work. In my opinion it's not worth the hassle. If your girlfriend is getting upset due to you having a number in your phone, do the right thing and remove the number.