Form Elements - user adding dynamically

I'm constructing an HTML form (via PHP) in which I want the user to be able to add or delete elements as needed. For instance, in a page detailing user information, the user might have one phone or several. Rather than having a set number of slots for phone numbers I'd have one slot and have a button by which the user could add a slot. The user could also delete a number in a similar manner. The design goal is something like Apple's iTools web page construction tool. Beside each slot is a "-" and a "+" to delete that slot or to add another one just under the existing slot. I've got something worked out that is beginning to work, but I wondered if anyone on the list had faced a similar problem or knows of an example script that handles a problem like that. Thanks, Nelson