Or select contact/menu/more/Set speed dial.
Or, from the manual (adapted so it makes sense):
1. Press HOME, then tap Phone.
2. Press MENU, and then tap Speed dial > add new.
3. Enter the name of the contact you want to add.
4. On the Speed dial screen, select the phone number of the contact you want to use, and allocate the speed dial number. Tap save.
