Now, cheap SIMs are getting popular like UQ mobile or Y mobile. It is possible that it will cost around 2,000 or 3,000 yen. There is no big difference from major cellphone companies about areas you can use it in.

Demerit is that most of cheap SIM companies accept only credit card payment not cash.  Also, services are limited like the unavailability of unlimited call.

Cost will be a little high or expensive but there are some SIM for visitors or foreign travelers.  It can be used in a short time like 7 days, 15 days, and 30 days. 

You can buy one in a major appliance store near a major station.

You can use it but please be careful about some matters below.

Before you leave Japan, check the setting of data roaming. If it is ON, when you arrive in Philippines, it automatically starts data roaming.  It will cost very high.  

So, before you leave Japan, turn off data roaming on setting. In the Philippines, you better use Philippine SIM like Globe or Smart.

But one thing you have to know, many cellphones sold in Japan are SIM locked.  If your cellphone is SIM locked, you might not be able to change SIM.

Yes. It is possible. Cellphone companies above and some telecommunication companies provide mobile WiFi (in Japan, it is called Pocket WiFi).  

But, you need apply with documents required by the company. (requirement depends on the company. )

It is impossible for visitors but if you live in Japan, it is possible to have one.
But, you need to prepare some documents. There are big 3 cellphone companies, DOCOMO, SoftBank, and AU. Let’s see the case of DOCOMO: Documents to submit

MY NUMBER CARD ( Please inquire about this card in the city hall. )
If expired date is within 3 months, payable only with your own credit card.

One of public IDs below
1) Health Insurance Card ( Kenko Hoken sho)
2) Basic resident register card ( Jumin Kihon Daicho card ) with photo
If expired date is within 3 months, payable only with your own credit card.
3) Alien Registration Card or Resident Card ( Gaikokujin Toroku shoumeisho or Zairyu card)

If your stay is less than 3 months, payable only with your own credit card.
Others can pay with the bill sent by DOCOMO.