I often use my iPhone as music player, travelling around the city with my headphones and answering calls by clicking the microphone. I was looking for a way to announce Caller ID, and was surprised there's only this hint here and it doesn't use built in speech technology.

This process could be scripted somehow, but as I didn't need hundreds of contacts, I just created them one by one. The described process is, however, optimized, taking only about 20 seconds per person.

First, open GarageBand and create a loop of desired length. I chose just about six bars. Then place your favorite ringtone sound (I used one from GarageBand's Library, found in Sound Effects » Work/Home » Cell Phone Ringing, and boosted its volume a bit) and place it at the second bar.

1. Copy the person's name in Address Book.
2. Paste it to Terminal as part of this command: say -o ~/Desktop/Output.aiff [paste person's name here]. Note that the Up Arrow key reveals the last command used, so later you can backspace the previous name and paste a new one.
3. Drag the Output file on your desktop to GarageBand on the first bar of your composition.
4. In GarageBand, choose File » Save As..., and again paste person's name as the filename (it's not important where it's saved).
5. Then select Share » Send Ringtone To iTunes.

The ringtone will play in iTunes so you can move on to another person. Finally, synchronize your iPhone with your iTunes, and assign the ringtones to your favorite people.

Now, I didn't spend much time on this at all, and it could be in the next version of iPhone software (I did submit it as an enhancement request) -- perhaps activated by a setting in the iPhone preferences. We'll soon find out, I guess.