Buttons at buttom of PhoneButtons at the bottom of the Phone screen give you quick access to your favorites, recent calls, your contacts, and a numeric keypad for dialing manually.

Call someone in your contacts list:
Tap Contacts, choose a contact, then tap a phone number.
Call a favorite:
Tap Favorites, then choose a contact.
Return a recent call:
Tap Recents, then tap a name or number in the list.
Dial a number:
Tap Keypad, enter the number, then tap Call.
Jump to favorites from anywhere:
Double-click the Home button.
Bring up the last number you dialed:
Tap Keypad, then tap Call. Tap Call again to dial the number.

http://www.apple.com/iphone/tips/