Can I use a phone from one carrier with a sim from another carrier?

I brought a phone from home which worked with a sim from bic camera (2,325 yen a month! :)) Unfortunately, now the phone is dying and I need a new one. I saw a really cheap phone from freetel which has an added bonus of being dual sim (so I can keep my home number for whatsapp) but I want to know if the freetel phone would work with the bic sim that’s on docomo’s network. Do you know?

Buy an unlocked phone, then you won’t be restricted to the carrier (or need to get them to unlock it).