Due to different technologies, mobile phones from your home country may not work in Japan. Most importantly, there is no GSM network, so GSM phones do not work. So if you come to Japan there are two things that are required for your phone to work:
1. Compatibility with the Japanese mobile phone network - The only foreign phones that
work in Japan are some 3G models; however the number of compatible phones is
increasing. Contact your service provider for details concerning your particular phone.
2. International roaming plan or rental SIM card - With an international roaming plan (from your home service provider) you use your own phone and number, but are charged international roaming rates which tend to be expensive. Alternatively, with a rental SIM card (from a Japanese provider) you use your own phone with a Japanese phone number and lower rates
So, you can buy or rent a phone in Japan. In Japan the cell phone prices vary by store but as much as $100. The general rule is supposed to be if you go to a big area like Shibuya or Shinjuku, since they are crowded and get lots of business they can charge higher prices. If you go out to a smaller store at a smaller station you'll get a better price. The AU Casio phone with the camera and GPS was at most places 35000 yen. It really depends on the phone and the place though. Phones range from free to 30000 yen (About $250). Generally the very newest phones (within the last 6 months) are $250. Those are the top of the line phones.
In Japan, conventional land line phone lines have be bought or rented. Buying a new phone line costs around 35,000 Yen, while rental a phone line from MyJapanPhone is much cheaper. If you want to know more rental details, please Click Here