SIM cards VOIP for foreigner worker in Japan

Hi, I will be dispatch to Osaka for 1 Years, and I am wondering about postpaid sim card in Japan. I already searching in google, but mostly offer bundling with phone.
I have unlocked phone, so I need VOIP Simcard. Anyone knows, how to buy it? Where to buy it? What is the best providers? What terms I need to concern about the subscribe?

Thank you in advance for all response.

Just dont signup with the phone. Just signup for SIM only.
https://tokyocheapo.com/business/internet/japan-sim-card-options-data-...
Read this ..

I use OCN 10GB monthly 3000 yen.
Contract can be stopped after 6 months when ever and plan can be changed every 1 month. So if you less data or more data you can adjust.

You get free 050 application which is VIOP only

http://www.ntt.com/en/personal.html

Thank you for all responses. I decide that I will use OCN Mobile, but if I buy the postpaid Simcard from Bic Camera, can we directly activate the Simcard at Bic Camera store?

Thank you.