When calculating the bandwidth required on a link for a VoIP connection, I have not seen any consideration for Layer 2 (Data Link) protocols or silence suppression. The Cisco calculator page ignores both.
DSL could incur significant overhead in the PPPoE link layer, reducing the call capacity. Ethernet service such as VLAN will see the ENET header on each packet. And don’t forget the required inter-frame interval for Enet, where applicable–that’s like extra bits in each frame.