There are other DNS providers that will do what you want with a purchased domain... you can also use afraid.org for that matter... I put up a domain I wanted others to be able to use for dyndns on afraid.org ...
I remember seeing something about using my own domain on afraid.org. However I use google apps, and I wasn't sure if it was possible or what it would take to keep my email hosted there while still using the dynamic dns. Honestly I don'y have much experience in this area and I don't really know what to research to learn more.
