If you've been adding to your address book for years in a program like Microsoft Outlook or Mac OS X's Address Book, you're just a sync away from porting all that accumulated data right over to your iPhone. Once there, info like phone numbers and email addresses show up as links, so you can reach out and tap someone.
Here's how to sync up your contacts with the iPhone. The steps are slightly different depending on which program you keep them in.
With the iPhone plugged into the computer, click its icon in the iTunes source list, then click the Info tab in the main part of the window. Turn on Sync contacts from:, and, from the pop-up menu, choose Outlook. Finally, click Apply.
Note that some of the more obscure data fields Outlook lets you use, like "Radio" and "Telex," won't show up on the iPhone. All the major data points, however, like name, email address, and (most importantly) phone number, do.
If Outlook gives you grief and error messages, you might be missing the necessary plug-in. Visit http://tinyurl.com/2lff4y for Apple's tips on getting it to play nice with the iPhone.
Microsoft's free email app for Windows stores your contacts in a file called the Windows Address Book. With the iPhone plugged into the computer, click its icon in the iTunes source list, and then click the Info tab in the main part of the window.
Turn on Sync contacts from:, choose Windows Address Book from the pop-up menu, and click Apply.