The trip will take over 4 hours - I think the Narita Express from Narita Airport to Tokyo station is over 1 hr, and then the transfer will take about 30 minutes, then a 2.5 hr bullet train. You can buy one ticket for the whole journey, and the ticket booth in Narita Airport generally has people who speak good English!
If you are flying from DFW (assuming this is after AA's KIX service ends), I see the logic on going to NRT and taking the train, it's definitely easier than flying a domestic leg to Osaka.