Some router/NM combinations will not support the VWIC2. If supported you have 1 channel group per port. So the max is 2.
http://www.cisco.com/en/US/customer/products/hw/routers/ps274/products_tech_note09186a00800b6e0f.shtml
The 3600 NM-1E2W, NM-1E1R2W, and NM-2E2W support one serial channel group per WIC slot. Therefore, there is no support for the VWIC-2MFT-E1.
The NM-1FE2W, NM-1FE1R2W, NM-2FE2W, and NM-2W support two serial channel groups per WIC slot. Therefore, there is support for VWIC-2MFT-E1.
