We do not use Constant Contact to acquire customers or building the email list.
Our application signup process collects a members email.
Once we have the emails, we manually create the lists and upload them to Constant Contact and send our mailers.
Wondering if we can make our application and ConstantContact talk in realtime where as soon as a user signus up through our application, his/her email is also pushed to the constant contact email list.
You most certainly can automate the process of doing this with your application. I highly suggest taking a look at our API documentation at the top of the page as well as our Code Samples as it will give you the proper equipment to get the job done.
Let me know if you need any help.