I'm using a bundle CISCO2821-CCME/K9 (PVDM2-32). I have a number of IP telephones connected to the router through a switch. I also want to connect to a PABX through a router E1 interface to interoperate with my IP telephones. For the PABX connection I would like to use a cheap VWIC-2MFT-E1 interface card installed in a HWIC slot. Does it work or am I obliged to install an expensive NM-HDV-1E1-30E network card in a NME slot, hosting inside the VWIC-2MFT-E1 interface card? If the NM card is not absolutely necessary, how many voice communications at G.711 and how many at G.729 may I establish simultaneously through the VWIC-2MFT-E1 interface card (having a PVDM2-32)?
The reason anyone uses the NM-HDV modules is to host the DSP resources. The 2600 series routers did not have on-board DSP slots, so the only way to put DSP's on them was via a network module or advanced integration module (AIM). So with the 2800 series, the only reason to use a NM-HDV module is if you need more than the chassis supports, which would only be true if you were doing a massive amount of transcoding or conference bridging, on top of support voice ports. And yes, the DSP calculator is your best option for figuring out if that PVDM2-32 will suffice.