I am not currently aware of any customers that are using this CMS that have integrated with Constant Contact, but judging by the information I've gathered from their website this would certainly be possible. It seems like you would be looking to build a TYPO3 extension that would utilize our API to perform whatever actions you're looking to do.
While we do not have any specific integration with TYPO3, this does appear to be a PHP based CMS, so you may find some of the code on our Code Samples page to be helpful in accomplishing your goals.
If you have any questions regarding our API's functionality or are having difficulties implementing it, please let us know and we will be happy to help. Thanks!