Tokyo Organized and crowded
The Yamanote Line (山手線, Yamanote-sen) is Tokyo's most important train line. It is a circular line, which connects Tokyo's major city centers. A trip around the whole circle takes approximately one hour.
Even though a single train on the Yamanote Line is roughly 200 meters long, there are departures about every two to four minutes in each direction.
Your phone works just fine in Tokyo on cellular wifi with your carrier (ATT for me)- I also had a portable wifi that you can get at the airport that works great, if your plan with your carrier in the US doesn't allow or charges too much. You can't change sim cards, since apparently its a different frequency in Japan.
Google maps is very helpful and will take you anywhere you want to go- as the subway system is a spider web. Totally organized, and they have attendants that can help you.