Is Christmas coming early this year ? Where do I start.......

Voicemail - Residential virtual numbers have them. After a set number of rings the calls forward to Voipo voicemail.
ACR - ability to block anymous/private/blocked calls. Since these are by-the-minute DID's we should be able to block calls that count against those minutes
FREE SIP Forwarding - Only 1 provider in all of the VoIP world charges for SIP forwarding, and they charge like .001 cpm.

More to come, these were just off the top of my head.