Hi John,
The full compatibility info can be found here;
http://www.cisco.com/c/en/us/support/docs/routers/2600-series-multiservice-platforms/5111-voice-comp-matrix.html
I believe the problem you are seeing is because this is a "WIC" card rather than "VIC or VWIC"
"Cisco Voice Network Modules provide enterprises, managed service providers, and service providers the ability to directly connect the public switched telephone network (PSTN) and legacy telephony equipment to existing Cisco 2600, Cisco 3600, and Cisco 3700 routers. The NM-1V and NM-2V carrier modules support Voice Interface Cards (VICs) to provide this connectivity.
Note: The NM-1V and NM-2V carrier modules do not support WAN Interface Cards (WICs), which are data-only interface cards. The "V" in the product name indicates that these are voice carrier modules. The WIC carrier module product numbers are NM-1W and NM-2W."
From;
http://www.cisco.com/c/en/us/support/docs/interfaces-modules/nm-2v-two-voice-fax-interface-card-slot-network-module/8016-hw-voice-net.html
Cheers!
Rob