5jgibbs,
It would help if we knew what
EXACTLY you are trying to do with "voice" since you talk about CCNA -
"I am studying for the CCNA and I know that's not applicable, but just for some fun." What are you trying to do for "fun", setup a voice lab, setup VoIP at home?????
Having taught CCNA for 10 years in a Cisco Network Academy, I would focus on your CCNA lab, the CCNA is complex enough without adding alot of VoIP stuff
Once you have your CCNA, with the 3640, which is a good router for CCNA or CCNP as well as any of the voice tracts, you can add the right modules, WICs, phones and software and have a voice lab. If you look at some of my posts , you will see that I have discussed a Voice lab recently and I have links to Ebay with some labs listed that you can look at for an example of just some of what is involved.However, it gets very complex, very quickly

this is why I said to focus on the CCNA and get a VERY SOLID FOUNDATION!!!!!
Just some thoughts!
E.A. Broda
CCNA, CCDA, CCAI, Network +