If it's a 3GS running iOS 5 or higher, you can set up the same iCloud account on your iPad and your iPhone and sync your notes. This explains how to set this up: http://www.apple.com/icloud/setup/ios.html. This is explained here: http://support.apple.com/kb/HT4191.
If it's an 3G, it can't use iCloud as it can't be updated beyond iOS 4.2.1. In that case you would have to sync your notes with a supported program on your computer (such as Outlook or Mac Mail) by selecting to do so on the Info tab of your iTunes sync settings, then sync them to your iPad; or you can email them to yourself and read the email on your iPad. (To get them in your Notes app on your iPad, you would have to cut and paste the text of each note into a new Note on your iPad.)
I'd use the iCloud method only if you already have your iPhone notes synced with the iCloud. Then, just enable iCloud notes sync on your iPad.
Note that if you still haven't enabled iCloud notes sync on your iPhone, the notes which are already on your iPhone will not get pushed to your iCloud account even after you enable it. Unfortunately, iCloud Notes sync does not work the same way as iCloud Contacts sync does.
Do you use iCloud on your iPhone?