This is a lame work-around...

To get numbers into the native phonebook, you could send the number in a Text Notification from a J2ME app to the target handset. Once received, the user may have the option of extracting the phone number and saving it to the phonebook. For example, my Sanyo 4900 can extract phone numbers, e-mail addresses, and web addresses from Text Notifications.

You could also get numbers into the phonebook by using the wtai interface to dial the number and then extracting the number from the call history logs.

To get numbers from the phonebook, well, that's kind of hard. You really need a data cable and some PC software. I don't know any other way to extract numbers from my 4900.

You can get e-mail addresses from the phonebook by sending an e-mail to that person with a CC to your dummy account (again). A J2ME app could then retrieve the message from the dummy account and extract the recipient's e-mail address.

I can't think of a way to get web addresses.

The common theme in these approaches is to use network access and server side processing to move data in and out of Java MIDlets. This is really the only I/O that MIDP 1.0 offers.