custom web ui

For the package creation process, yes. For the actual signing session, this must be embedded into your application in an iFrame. Now, this can be completely branded/white labeled to make it appear as if part of your application, but the signing ceremony cannot be tampered with. Everything else can be customized. You could also embed the designer session within your application, in an iFrame, if you simply wanted to make it look like e-SignLive was a part of your portal. Hopefully this answers your question. Let me know.

Is it possible to get an example that uses iframe.

If you are using Java, you can try this project: http://bit.ly/esljavaexample It has several examples inside the code and a setting for a demo using an iframe. Please let me know if this was helpful!