1. Tap the Phone icon.
2. Tap the Recents soft key along the bottom.
3. TIP: Any phone number you see listed is not yet in your Contacts list. You see names instead of phone numbers when they are already in your Contacts list.
4. Tap the blue arrow at the right edge of the phone number to see the Info screen shown to the right.
5. Scroll down and tap Create New Contact or Add to Existing Contact.
Source: Chapter 10: Your iPhone as a Phone,