[TYPO3] How to create (simple) forms as content elements?

[Martin Kindler]

I have been trying for some days now to solve this (seemingly) trivial
problem with Typo3:
create a content element which contains a little form (in my case just one
text input element to contain a phone number) which should be processed by
some (possibly external) action.

What is best practice to do this?
I have explored the following possibilities:
- (ab)use the form (sic!) wizard, but it seems only to be capable of forms
with a "mailto"-action
- use a plain HTML element (this is the way I have chosen to use, but it is
ugly!!!)
- write a tiny extension to do it (I have written this extension, but it
just is overkill)

Did I miss something? How do you do it?

Martin