Debbie,
Great question. I think it's a little more challenging growing your email list through telecourses. We have had great success getting more e-letter subscribers through our blogging and marketing with e-newsletters workshops. But 1) we have that face-to-face contact at live events and 2) the newsletter content supplements and expands on topics we cover in the workshops. We also send a direct link to our archives so they can check out the quality of the product and sign up easily if they like what they see. The result: we are building our opt-in list and, when we have developed credibility with our subscribers, we can send them offers from time to time.
It also depends, I think, on whether value is perceived. Some people develop a list just to inform people of their upcoming workshops. There is nothing wrong with this, but it is not always perceived as valuable.
On the other hand, you may have a very helpful e-newsletter that subscribers to your list will get. If your telecourse touches on the same rich content, I would subtly tie that content to your newsletter content. (In the telecourse, when you talk about XYZ, tell people that your free newsletter expands on this topic and provides more tips/ strategies for doing ______.)
That way, at the end of your telecourse, you can send an email with a direct link to sign up. It also helps if people can see an example of what they will be getting. (For us, it''s our e-letter archives we send them to, where there is a simple e-letter sign-up form, too.)
If through the telecourse, you can show them that the wonderful stuff they got will continue when they join your list, they will be more likely to sign up. Don't be shy about just asking them to join!

