By default, when you make an outgoing call on your iPhone your phone number appears to the person you call -- assuming her phone is capable of displaying it. You can make your number private by changing the caller ID settings on your device. iPhone also has incoming caller ID. The name and photo of your contact will show up on the screen of your iPhone each time she calls you.
Go to the "Settings" application on your iPhone's home page.
Tap "Phone" and then "Show My Caller ID" in the "Calls" section.
Choose your preference. Toggle the caller ID feature between "On" and "Off" by tapping the icon next to "Show My Caller ID." When it's in the "Off" position, your phone number will not be visible to your callers.
Change the information for the incoming caller ID associated with your contacts by going to the "Contacts" application and tapping on the name of a contact. Tap the "Edit" icon at the top of the page and type in the name you want to appear when the person calls you.
Add a picture to a contact's caller ID by tapping on the "Add Photo" icon, and then either taking a new photo, or choosing one from your camera roll. Tap "Done" in the top right corner of the contact's profile when you're satisfied with the changes you made.