If you go into the address book and click on on the name tab in front of a phone number you can select "Large Type" and have the number displayed all the way across your screen

In addition to Large Type on phone numbers, Address Book has lots other tricks up its sleeve. For instance, if you click on the tab in front of an address you can select "Map of" to open that address in Mapquest in your default browser (see after the jump). As we mentioned a while back, there's also a plugin to add Google Maps to this as well. With the appropriate Bluetooth phone Address Book can send SMS messages and dial numbers. You can even print out a pocket sized address book. If you haven't done so, check out the Address Book help for all these tips and more