The Talkmate does connect to some kind of cartridge on the 410. The cable from the Talkmate has 4 leads, and two leads connect to T and R on the cartridge and the other two appear to connect to background music.

I do not know anything about the 410, but the T and R leads on the cartridge do not appear to be a CO line interface. But if you guys think it will work, I will give it a try as I will have a free CO line port available on the NEC.