Kevin Wallace (CCIE #7945, CCSI# 20061) has recently done a couple of webcasts for Pearson IP Certification that discuss both analog and digital voice ports. The replays are posted at Network World.
Each video is over 30 minutes in length and would benefit students pursuing both the CCNA Voice and CCNP Voice certifications. For CCNP Voice students, the material specifically covers topics included on the CVOICE (642-437) exam.
Watch the videos below:
Cisco CCNP Voice VoIP Fundamentals (CVOICE): Analog Voice Ports
Cisco CCNP Voice VoIP Fundamentals (CVOICE): Digital Voice Ports