Here is some information for my fellow travelers on Communication from and in Japan

By phone

Emergency call
Emergency call can be made from any phone at free of charge:call 110 for
police or call 119 for fire and ambulance.

Pay telephones
Public pay telephones (公衆電話 kōshū denwa) are easily found, particularly near train stations, although with the popularity of mobile phones, public pay phones are not as quite as numerous as they once were. Gray and green pay phones accept ¥10 and ¥100 coins, and pre-paid cards. Some of the gray phones, as indicated on the LCD display, can make international calls. Another type of phone, IC pay phones, use an different IC-type card, but all can make international calls. Both types of pre-paid cards may be purchased at convenience stores, train station kiosk stores and sometimes in vending machines next to the phone. International phone charges from pay phones can be unusually high; third-party phone cards are a reasonable alternative.

Mobile phones
Japanese mobile phone (携帯電話 keitai denwa or just keitai) standards are largely incompatible with those in the rest of the world, so it is unlikely your mobile phone will work in Japan. However, if you have a 3G phone and a carrier that roams with Vodafone (Vodafone Roaming Partners), your phone should work on their WCDMA network. Also, some of Vodafone's newer 3G models accept GSM SIM cards and thus you can use your usual phone number while in Japan.
Travelers on extended trips can purchase a mobile phone on monthly contract with a major credit card, which can work out to be cheaper than a rental phone for longer durations. The major mobile carriers in Japan are NTT DoCoMo, KDDI's au and Vodafone. Expect to pay around around ¥5000 per month, assuming light calling; a cancellation fee may apply when the contract is terminated. Prepaid mobile phones were previously an economical option for visits of over a few weeks or so, but now they are no longer available to tourists and require either a Japanese passport or an alien registration card.

By mail
You can send postcards to anywhere in the world for 70 yen. Public mail deposit boxes are found throughout Japan. They have two slots, one for regular domestic mail, and the other for overseas and express mail.

By net
Internet cafes (インターネットカフェ) can be found in or around many train stations. Here, you can upload your pictures from a digital camera, and if you forgot your cable, some cafes will lend you a memory card reader for free. Manga coffee shops (漫画喫茶 manga-kissa) usually have internet PCs as well. When you get tired of browsing the web, you can browse comic books, watch TV or play video games. The cost is typically around ¥400/hour, with free drinks. Often they have special night fare around ¥1500 for the 4-5 hour period when no trains are running. Internet cafes can be a safe and inexpensive place to spend the night if you miss the last train.
A number of Business Hotels have internet access available if you have your own computer, sometimes for free. In most cases, access is usually provided by a VDSL modem connected to the hotel telephone system. Please beware that some of the hotels that offer free internet access do not include the rental for the modem in the "free" part of the service, so check before you use. Setting up your network interface for DHCP is usually all that is required to gain access to the internet in such situations. Many also tend to have rental or free PC's available for hotel guests.
Some larger train stations and airports also have rental PCs to netsurf and send e-mail, usually about ¥100 (coin) for 10 minutes.
When using public access PC's, remember to be careful not to the accidentally hit the left side Alt-Shift keys together, or you'll be writing in Japanese—even if you don't know any. On the other hand, if the last person left the computer this way, you can use this key combination to switch back to the Roman alphabet. It is also possible to find Wi-Fi "hot spots" around many large cities in Japan, especially near tech-related businesses and large corporate buildings with unsecured wireless networks (the Apple store in Ginza, Tokyo has a fast, open 802.11g connection).