Quick question, I've noticed some things online and wanted this clarified. I have a Cisco1720 router in place as of now. I'm upgrading to a Cisco 2821. Can I use a module from the 1720 in the 2821?
As far for the WICs used by the 1720, they are not all supported, and for NM (1720 don't supported NM anyways) not all NMs are supported on the 2800 either: